Denison Reports Financial and Operational Results for Q1 2025, Highlighted by Continued Advancement of the Phoenix Project, and the Results of its Shareholder Meeting

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Denison Mines Corp.

1100 – 40 University Ave

Toronto, ON M5J 1T1

www.denisonmines.com

PRESS RELEASE

Denison Reports Financial and Operational Results for Q1 2025,

Highlighted by Continued Advancement of the Phoenix Project, and

the Results of its Shareholder Meeting

Toronto, ON – May 12, 2025. Denison Mines Corp. (‘Denison’ or the ‘Company’) (TSX: DML, NYSE American: DNN)

today filed its Condensed Consolidated Financial Statements and Management’s Discussion & Analysis (‘MD&A’) for

the quarter ended March 31, 2025. Both documents w ill be available on the Company’s website (at

www.denisonmines.com), SEDAR+ (at www.sedarplus.ca) and EDGAR (at www.sec.gov/edgar). The highlights

provided below are derived from these documents and sho uld be read in conjunction with them. All amounts in this

release are in Canadian dollars unless otherwise stated.

David Cates, President and CEO of Denison commented, “With the Canadian Nuclear Safety Commission ('CNSC')

announcing in Q1’2025 the scheduling of a public hearing ('Hearing') for our flagship Phoenix In-Situ Recovery ('ISR')

project in late 2025, our focus for the remainder of the year has shifted to completion of the detailed design engineering

phase and advancement of construction planning and procur ement efforts. Our plans are designed to put us in a

position to start construction in early 2026, following anticipated regulatory approvals. Based on this timeline, we expect

to be able to maintain our previous guidance of first production from Phoenix by mid-2028, which would make Phoenix

the first new large-scale uranium mine in northern Sa skatchewan since the Cigar Lake mine was commissioned in

2014.

By the end of Q1’2025, we have achieved approximately 75% completion of total engineering for Phoenix, and we have

already funded over $7 million and committed a further $67 million for long-lead capital purchases. With 2.2 million

pounds U3O8 in physical uranium holdings on hand, a strong cash balance, and no debt, Denison remains in an enviable

financial position – able to fund both (i) our pre-Final Inve stment Decision ('FID') inves tments in Phoenix and (ii)

important potential future growth initiatives.

At our McClean Lake Joint Venture ('MLJV') with Orano Canada, we are expecting 2025 to be a notable year with the

commencement of mining at the McClean North deposit using the MLJV’s patented Surface Access Borehole Resource

Extraction ('SABRE') mining method. Thus far this year, si te preparation activities have recommenced and we are

expecting mining to commence in the coming months.

In addition to our planned investments in the Company’s project development portfolio, we are working to amplify our

exposure to exploration discovery. With that objective we entered into agreements with Cosa Resources Corp. ('Cosa')

(TSX-V: COSA) in Q1’2025 and Foremost Clean Energy ('Foremost') (NASDAQ:FMST) (CSE:FAT) in Q4’2024, both

of which involve collaborating on the exploration of several of Denison's non-core properties. Initial exploration results

from this strategy are encouraging – as Cosa has already id entified a two-kilometre strike extension of the Hurricane

Trend through its initial drilling program at the Murphy Lake North uranium property, and Foremost has reported a new

discovery of uranium mineralization at the Hatchet Lake uranium property.

At the corporate level, during the quar ter, we welcomed Ken Hartwick, who previously served as the CEO of Ontario

Power Generation, and Jinsu Baik, KHNP Canada Energy Ltd. ’s nominee, to the Denison board of directors. We

believe Ken and Jinsu will bolster the breadth of nuclear industry and commercial knowledge on our Board and enhance

its oversight during the critical process of Phoenix project execution and marketing of our future uranium production.

We are also pleased to welcome Wes Carson, Vice Presi dent, Mining Operations at Wheaton Precious Metals Corp.,

to the Denison board today, after his election at Denison’s annual and special shareholders meeting. Wes enhances

the depth of technical expertise on our Board, as he brings a wealth of mining industry experience and best practices,

having held a variety of leadership roles in operations, project development, and engineering.”

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Highlights

 Regulatory Approval Hearing Dates set for the Phoenix ISR Project Supporting Guidance for First Production

by First Half of 2028

The Canadian Nuclear Safety Commission (‘CNSC’) Registrar announced the schedule for the CNSC public hearing

(the ‘Hearing’) for the Wheeler River Uranium Project (‘Wheeler River’). The Hearing is scheduled to be held in two

parts (October 8, 2025, and December 8 to 12, 2025) and represents the final step in the federal approval process

for the Wheeler River Project’s (‘Project’) Environmental Assessment (‘EA’) and the Licence to Prepare and Construct

a Uranium Mine and Mill (‘Licence’). The Hearing dates are expected to supp ort commencement of construction in

early 2026 and first production in the first half of 2028, consistent with past guidance.

The announcement of the Hearing schedule follows the successful completion of multiple key regulatory milestones

in late 2024, including (i) completion of the technical review phase of the federal EA approval process in November,

(ii) acceptance by the CNSC of the Co mpany's final Environmental Impact St atement (‘EIS’) for the Project in

December, and (iii) the CNSC's determination of the sufficiency of Denison's Licence application, also in November.

These accomplishments indicate that the CSNC staff s upport the advancement of the Pr oject and are transitioning

their efforts to prepare an evidence-based summary report for the Commission members that will govern the Hearing

and render their decision on the EA and Licence once the Hearing is complete.

 Achieved 75% Completion of Total Engineering for Phoenix

In January 2024, Denison awarded a contract to Wood Canada Limited (‘Wood’), for the completion of a significant

portion of the detailed design engineeri ng for the Phoenix ISR project. The work commenced in the first quarter of

2024 and is expected to be substantially completed in the third quarter of 2025. Phoenix detailed design engineering

activities are an important element of the Company’s continued effort s on advancing Phoenix towards a final

investment decision (‘FID’), in support of its objective to achieve first production by the first half of 2028.

Total engineering completion at end of the first quarter of 2025 was approximately 75%, supported by finalization of

process design, piping and instrumentation diagrams (‘P&ID’s’), hazard and operability studies (‘HAZOPs’), selection

of major process equipment, electrical di stribution infrastructure and substant ially complete on civil engineering

design. The completion of the detailed design engineering has been scheduled to ensure Denison is ready to

commence project construction upon receipt of regulatory approval.

 McClean Lake Joint Venture Advances Site Preparation Activities for Planned 2025 SABRE Mining Program

Site preparation activities have recommenced at McClean North in preparation for the 2025 SABRE mining program.

Site development is on track to support the commencement of mining activities in mid-2025.

 Appointment of New Board Members

In March 2025, Denison announced the appointment of Ken Hartwick, who previously served as the CEO of Ontario

Power Generation ('OPG'). Mr. Hartwick's appointment comes following the retirement from the Board of Brian Edgar,

after having served as a Director of Denison and its prede cessors for over 20 years. Denison also reported the

appointment of Mr. Jinsu Baik to t he Board, replacing Mr. Jong Ho Hong as KHNP Canada Energy Ltd.’s ('KHNP

Canada’) nominated director to the Board. Additionally, Mr. Wes Carson, Vice President, Mining Operations at

Wheaton Precious Metals Corp., was appointed to the Boar d at the Corporation’s annual and special shareholder

meeting held on May 12, 2025.

 Formation of Exploration Joint Ventures with Cosa Resources Corp.

In January 2025, Denison completed an acquisition agreement with Cosa Resources Corp. (‘Cosa’) for Cosa to

acquire a 70% interest in three of Denison’s properties in the eastern portion of the Athabasca Basin region in

northern Saskatchewan in exchange for approximately 14.2 million Cosa common shares, $2.25M in deferred equity

consideration, and a commitment to spend $6.5 million in exploration expenditures on the properties. Upon the close

of the transaction, Denison became Co sa’s largest shareholder (representing ~19.95% ownership interest in Cosa

at that time) and Denison and Cosa formed three uranium exploration joint ventures.

2025 Annual & Special Shareholders Meeting

Denison is also pleased to report the passing of all item s of business presented to sh areholders at the Company’s

annual and special shareholders meeting held in Toronto today (the “ Meeting”), as disclosed in the management

information circular dated March 28, 2025. Detailed results of the vote by proxy for the election of directors are set out

below.

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Nominee Votes For % For Votes Withheld % Withheld

Jennifer Traub 367,438,77 0 94.99% 19,399,921 5.01%

David Cates 366,920,809 94.85% 19,917,881 5.15%

Jinsu Baik 384,502,960 99.40% 2,335,731 0.60%

Wes Carson 366,457,344 94.73% 20,381,346 5.27%

Ken Hartwick 384,596,39 6 99.42% 2,242,294 0.58%

David Neuburger 379,319,168 98.06 % 7,519,522 1.94%

Laurie Sterritt 378,238,67 9 97.78% 8,600,011 2.22%

Patricia Volker 379,592,941 98.13 % 7,245,749 1.87%

The Company has provided more details on the results of all matters considered at the Meeting in its Report of Voting

Results which has been filed under its profile on SEDAR+ at www.sedarplus.ca and on EDGAR at www.sec.gov/edgar.

About Denison

Denison Mines Corp. was formed under the laws of Ontario and is a reporting issuer in all Canadian provinces and

territories. Denison’s common shares are listed on the To ronto Stock Exchange (the ‘TSX’) under the symbol ‘DML’

and on the NYSE American exchange under the symbol ‘DNN’.

Denison is a leading uranium mining, development, and exploration company with interests focused in the Athabasca

Basin region of northern Saskatchewan, Canada. Denison has an effective 95% interest in its flagship Wheeler River

Uranium Project, which is the largest undeveloped uranium proj ect in the infrastructure rich eastern portion of the

Athabasca Basin region of northern Saskatchewan. In mid-2 023, the Phoenix feasibility study was completed for the

Phoenix deposit as an ISR mining operation, and an update to the previously prepared 2018 Pre-Feasibility Study

('PFS') was completed for Wheeler River's Gryphon deposit as a conventional underground mining operation. Based

on the respective studies, both deposits ha ve the potential to be competitive wit h the lowest cost uranium mining

operations in the world. Permitting efforts for the plan ned Phoenix ISR operation commenced in 2019 and several

notable milestones were achieved in 2024 with the submissi on of federal licensing documents and the acceptance of

the final form of the project’s Environmental Impact Stat ement by the Province of Saskatchewan and the Canadian

Nuclear Safety Commission.

Denison's interests in Saskatchewan also include a 22.5% ownership interest in the McClean Lake Joint Venture

('MLJV'), which includes unmined uranium deposits (pla nned for extraction via the MLJV's SABRE mining method

starting in 2025) and the McClean Lake uranium mill (currently utilizing a portion of its licensed capacity to process the

ore from the Cigar Lake mine under a toll milling agreement) , plus a 25.17% interest in the Midwest Joint Venture

Midwest Main and Midwest A deposits, and a 70.55% interest in the Tthe Heldeth Túé ('THT') and Huskie deposits on

the Waterbury Lake Property. The Midwest Main, Midwest A, THT and Huskie deposits are located within 20 kilometres

of the McClean Lake mill. Taken together, Denison has direct ownership interests in properties covering ~384,000

hectares in the Athabasca Basin region.

Additionally, through its 50% ownership of JCU (Canada) Exploration Company, Limited ('JCU'), Denison holds

interests in various uranium project joint ventures in Ca nada, including the Millennium project (JCU, 30.099%), the

Kiggavik project (JCU, 33.8118) and Christie Lake (JCU, 34.4508%).

In 2024, Denison celebrated its 70th year in uranium mining, exploration, and development, which began in 1954 with

Denison’s first acquisition of mining claims in the Elliot Lake region of northern Ontario.

Technical Disclosure and Qualified Person

The technical information contained in this press release has been reviewed and approved by Chad Sorba, P.Geo.,

Denison’s Vice President Technical Services & Project Evaluation, who is a Qualified Persons in accordance with the

requirements of NI 43-101.

For more information, please contact

David Cates (416) 979-1991 ext. 362

President and Chief Executive Officer

Geoff Smith (416) 979-1991 ext. 358

Vice President Corporate Development & Commercial

Follow Denison on Twitter @DenisonMinesCo

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

Certain information contained in this pre ss release constitutes ‘forward-looking info rmation’, within the meaning of the applic able

United States and Canadian legislation conc erning the business, operations and financ ial performance and condition of Denison.

Generally, these forward-looking statements c an be identified by the use of forward-look ing terminology such as ‘plans’, ‘expects’,

‘budget’, ‘scheduled’, ‘estimates’, ‘forecasts’, ‘intends’, ‘anticipates’, or ‘believes’, or the negatives and/or variations of such words and

phrases, or state that certain actions, events or results ‘may’, ‘could’, ‘would’, ‘might’ or ‘will be taken’, ‘occur’, ‘be achieved’ or ‘has

the potential to’.

In particular, this press release contains forward-looking information pertaining to the following: projections with respect to exploration,

development and expansion plans and objectives, including the scope, objectives and interpretations of the FS, PFS and the Wheeler

River technical de-risking process for the proposed ISR operation for the Phoenix depos it; expectations with respect to the EA, EIS

and Licensing and permitting for pr oposed operations at Wheeler Rive r, including the Hearing; expec tations with respect to mine

development and operations on the Wheeler River property, including discussions of an FID and timing for construction and

achievement of first production; anticipated benefits of the transactions with Foremost and Cosa; expectations regarding the re start

of mining operations at McClean Lake; expectations regarding the performance of the uranium market and global sentiment regarding

nuclear energy; and expectations regarding Denison’s joint venture ownership interests. Statements relating to ‘mineral reserves’ or

‘mineral resources’ are deemed to be forward-looking information, as they involve the implied assessment, based on certain estimates

and assumptions that the mineral reserves and mineral resources described can be profitably produced in the future.

Forward-looking statements are based on the opinions and estimates of management as of the date such statements are made, and

they are subject to known and unknown risks, uncertainties and other factors that may c ause the actual results, level of activi ty,

performance or achievements of Denison to be materially different from those expre ssed or implied by such forward-looking

statements. For example, the results and underlying assumptions and interpretations of the FS and PFS may not be maintained after

further testing or be representative of ac tual conditions within the applicable deposit s. In addition, Denison may decide or ot herwise

be required to discontinue testing, evaluati on, engineering, and development work if it is unable to maintain or otherwise secu re the

necessary approvals or resources (such as testing facilities, capital funding, etc.). Denison believes that the expectations reflected in

this forward-looking information are reasonable, but no assurance can be given that these expectations will prove to be accurate and

results may differ materially from those anticipated in this fo rward-looking information. For a discussion in respect of risks and other

factors that could influence forward-looki ng events, please refer to the Annual Info rmation Form dated March 25, 2025 under the

heading ‘Risk Factors’. These factors are not, and should not be, construed as being exhaustive.

Accordingly, readers should not place undue re liance on forward-looking statements. The forward-looking information contained i n

this press release is expressly qualified by this cautionary statement. Any forward-looking information and the assumptions made with

respect thereto speaks only as of the date of this press release. Denison does not undertake any obligation to publicly update or revise

any forward-looking information after the date of this press rel ease to conform such information to actual results or to change s in

Denison's expectations except as otherwise required by applicable legislation.