IAMGOLD Announces Updated Resource Estimate at Nelligan - Growing Resources by 63% with 2.0 Million Gold Ounces in Indicated Resources and 3.2 Million Gold Ounces in Inferred Resources

Toronto, Ontario - IAMGOLD Corporation (TSX: IMG) (NYSE: IAG) ('IAMGOLD' or the 'Company') is pleased to announce an updated Mineral Resource Estimate ('MRE') for the Nelligan Joint Venture Project ('Nelligan') (IAMGOLD: 75%, Vanstar Mining Resources Inc. ('Vanstar'): 25%), located 60 kilometres southwest of Chibougamau, Quebec, Canada.

Highlights:

Nelligan Joint Venture Project updated MRE comprises (on a 100% basis using a US$1,500 per ounce gold price):

72.2 million tonnes of Indicated Mineral Resources averaging 0.85 grams of gold per tonne for 1.97 million ounces of gold

114.1 million tonnes of Inferred Mineral Resources averaging 0.88 grams of gold per tonne for 3.24 million ounces of gold

Mineral Resources have increased by 92% in tonnage, with a 15% decline in gold grades, for an overall gain of 63% in metal content - relative to the 2019 Mineral Resource estimate

Additional infill drilling completed from 2020 to 2022 and refinement of the deposit and structural models contributed to the conversion of 62% of Inferred Mineral Resources to an Indicated Mineral Resource category relative to the 2019 Mineral Resource estimate

Potential highlighted for further resource expansion

The estimate was completed in accordance with the Canadian Institute of Mining, Metallurgy and Petroleum ('CIM') Definition Standards incorporated by reference in National Instrument 43-101 - Standards of Disclosure for Mineral Projects ('NI 43-101').

Craig MacDougall, Executive Vice President, Growth for IAMGOLD, stated: 'We are very pleased to see that our drilling programs have confirmed the anticipated expansion potential at Nelligan resulting in a significant increase of Mineral Resources within a wide and persistent mineralized system. This Mineral Resource estimation has not only resulted in a significant increase in resources, but also resulted in upgrading nearly 2 million ounces from Inferred to an Indicated resource classification. Potential for further resource expansion appears favourable, noting that the deposit has areas within the resource pit shell, along strike and at depth that remain open for further drilling. Our exploration efforts continue to highlight the significance of this pure grass-root discovery.'

'I also want to commend the exploration team which has conducted the recent drilling programs safely and through challenging times with the wide ranging impacts of the COVID-19 pandemic, including costs increases and service availability across our industry. We also thank all of our service providers who have worked with us to contribute to the success of this project,' added Mr. MacDougall.

Since 2020, IAMGOLD has drilled 53 additional holes (for 22,045 metres) to expand the resource base particularly to the west and at depth. As at December 31, 2021, IAMGOLD had previously reported Mineral Resources at Nelligan (on a 100% basis) comprised of Inferred Mineral Resources of 97.0 million tonnes grading 1.02 g/t Au for 3.2 million contained ounces (see news releases dated October 22, 2019 and February 23, 2022). Relative to the 2019 MRE, the current estimated Mineral Resources have increased by 92% in tonnage, with a 15% decline in gold grades due to a reduction in the calculated cut-off grade from 0.50 g/t Au to 0.35 g/t Au, for an overall gain of 63% in contained gold.

The updated MRE for the Nelligan Project used all available validated data, and includes results incorporated into the resource model from the 2020 to 2022 drilling programs (53 holes for a total of 22,045 metres drilled), as well as an additional 24 historic drill holes previously located outside mineralized domains, for a total of 84,490 metres in 267 diamond drill holes. Drill holes are variably spaced from 35 to 100 metres apart in the core resource area. The deposit was modelled using Leapfrog to create domains using lithology, structure and alteration type (or assemblage) and intensity, with gold grade continuity analysis of each domain. The mineralized domain model comprises five (5) main gold-bearing domains (Renard Footwall, Renard, Z36, Liam and Dan) cut by a northeast-striking post-mineralization fault which locally cuts and offsets several domains.

The estimate was prepared using a block model approach (10.0 x 5.0 x 5.0 metres block dimensions) employing Ordinary Kriging (OK) interpolation constrained by 3D wireframes using hard domain boundaries during estimation. A Datamine Studio NPVS Scheduler Mine Planning Software was run on the block model to constrain the resource and to support the CIM requirement that Mineral Resources have 'reasonable prospects for eventual economic extraction'. Pit slopes in rock were assumed at 45-degree and at 18.4-degree in overburden and the resource estimate assumes a long-term gold price of US$1,500 per ounce. Gold recoveries are assumed at 83% as indicated by metallurgical test work completed to date. Only mineralization contained within the optimized pit shell has been included in the resource estimate. The resource estimate was completed by SRK Consulting (Canada) Ltd. ('SRK') with an effective date of December 31st, 2022 and is reported at a 0.35 g/t Au cut-off grade.

IAMGOLD will file an updated NI 43-101 technical report for the updated Mineral Resources estimation for Nelligan on SEDAR at www.sedar.com within 45 days of the date of this news release.

About IAMGOLD

IAMGOLD is an intermediate gold producer and developer based in Canada with three operating mines in North America, South America and West Africa. The Company is building the large-scale, long life Cote Gold project in Canada in partnership with Sumitomo Metals & Mining of Japan, which is expected to commence production in early 2024. IAMGOLD employs approximately 5,000 people and is committed to maintaining its culture of accountable mining through high standards of Environmental, Social and Governance ('ESG') practices, including its commitment to Zero Harm, in every aspect of its business. IAMGOLD is listed on the New York Stock Exchange (NYSE: IAG) and the Toronto Stock Exchange (TSX: IMG) and is one of the companies on the Jantzi Social Index ('JSI'), a socially screened market capitalization-weighted consisting of companies which pass a set of broadly based environmental, social and governance rating criteria.

Contact:

Investor

Graeme Jennings

Vice President

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CAUTIONARY NOTE TO U.S. INVESTORS REGARDING DISCLOSURE OF MINERAL RESOURCE ESTIMATES

The mineral resource estimates contained in this news release have been prepared in accordance with NI 43-101. These standards are similar to those used by the United States Securities and Exchange Commission (the 'SEC') Industry Guide No. 7, as interpreted by the SEC staff. However, the definitions in NI 43-101 differ in certain respects from those under Industry Guide No. 7. Accordingly, mineral resource information contained in this news release may not be comparable to similar information disclosed by United States companies.

As a result of the adoption of amendments to the SEC's disclosure rules (the 'SEC Modernization Rules'), which more closely align its disclosure requirements and policies for mining properties with current industry and global regulatory practices and standards, including NI 43-101, and which became effective on February 25, 2019, the SEC now recognizes estimates of 'measured Mineral Resources', 'Indicated Mineral Resources' and 'Inferred Mineral Resources.' In addition, the SEC has amended definitions of 'proven Mineral Reserves' and 'probable Mineral Reserves' in its amended rules, with definitions that are substantially similar to those used in NI 43-101. Issuers must begin to comply with these SEC Modernization Rules in their first fiscal year beginning on or after January 1, 2021, though Canadian issuers that report in the United States using the Multijurisdictional Disclosure System ('MJDS') may still use NI 43-101 rather than the SEC Modernization Rules when using the SEC's MJDS registration statement and annual report forms.

United States investors are cautioned that while the SEC now recognizes 'measured Mineral Resources', 'Indicated Mineral Resources' and 'Inferred Mineral Resources', investors should not assume that any part or all of the mineral deposits in these categories will ever be converted into a higher category of Mineral Resources or into Mineral Reserves. These terms have a great amount of uncertainty as to their economic and legal feasibility. Under Canadian regulations, estimates of Inferred Mineral Resources may not form the basis of feasibility or pre-feasibility studies, except in limited circumstances. Investors are cautioned not to assume that any 'measured Mineral Resources', 'Indicated Mineral Resources', or 'Inferred Mineral Resources' that the Company reports in this news release are or will be economically or legally mineable.

Further, 'Inferred Mineral Resources' have a great amount of uncertainty as to their existence and as to their economic and legal feasibility. It cannot be assumed that any part or all of an Inferred mineral resource will ever be upgraded to a higher category.

The mineral resource data set out in this news release are estimates, and no assurance can be given that the anticipated tonnages and grades will be achieved or that the Indicated level of recovery will be realized.

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION

This news release contains forward-looking statements. All statements, other than of historical fact, that address activities, events or developments that the Company believes, expects or anticipates will or may occur in the future are forward-looking statements. Forward-looking statements are generally identifiable by, but not limited to, the use of the words 'may', 'will', 'should', 'would', 'continue', 'expect', 'expected', 'budget', 'forecast', 'anticipate', 'estimate', 'believe', 'intend', 'appear' 'plan', 'schedule', 'guidance', 'outlook', 'potential', 'favourable', 'plans', 'targeted', or 'project' or the negative of these words or other variations on these words or comparable terminology. Forward-looking statements are subject to a number of risks and uncertainties, many of which are beyond the Company's ability to control or predict, that may cause the actual results to differ materially from those discussed in the forward-looking statements. Factors that could cause actual results or events to differ materially from current expectations include, among other things, without limitation, differences in the mineral content within the material identified as Mineral Resources or Mineral Reserves from that predicted, the failure to accurately estimate Mineral Resources or Mineral Reserves, unexpected increases in capital expenditures, operating expenditures and exploration expenditures, changes in development or mining plans due to changes in logistical, technical or other factors, the possibility that future exploration results will not be consistent with the Company's expectations, changes in world gold markets and other risks disclosed in IAMGOLD's most recent Form 40-F/ Annual Information Form on file with the United States Securities and Exchange Commission at https://www.sec.gov/edgar.shtml and Canadian securities regulatory authorities at www.sedar.com, which are incorporated herein. Any forward-looking statement speaks only as of the date on which it is made and, except as may be required by applicable securities laws, the Company disclaims any intent or obligation to update any forward-looking statement. The Company disclaims any intention or obligation to update or revise any forward-looking statements whether as a result of new information, future events or otherwise except as required by applicable law.

All material information on IAMGOLD can be found at www.sedar.com or at www.sec.gov.

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