Exhibit 99.1

ICON plc Set to Join Russell 3000^® Index

DUBLIN--(BUSINESS WIRE)--June 26, 2023--ICON plc, (NASDAQ: ICLR), is set to join the broad-market Russell 3000^® Index at the conclusion of the 2023 Russell indexes annual reconstitution, effective after the US market opens today, Monday, June 26.

Annual Russell indexes reconstitution captures the 4,000 largest US stocks as of April 28, ranking them by total market capitalization, including both the Russell 3000^® and Russell Microcap^® Indexes.

Membership in the US all-cap Russell 3000^® Index, which remains in place for one year, means automatic inclusion in the large-cap Russell 1000^® Index or small-cap Russell 2000^® Index as well as the appropriate growth and value style indexes. FTSE Russell determines membership for its Russell indexes primarily by objective, market-capitalization rankings and style attributes.

Russell indexes are widely used by investment managers and institutional investors for index funds and as benchmarks for active investment strategies. Approximately $12.1 trillion in assets are benchmarked against Russell’s US indexes. Russell indexes are part of FTSE Russell, a leading global index provider.

For more information on the Russell 3000^® Index and the Russell indexes reconstitution, go to the “Russell Reconstitution” section on the FTSE Russell website.

About ICON plc

ICON plc is a world-leading healthcare intelligence and clinical research organisation. From molecule to medicine, we advance clinical research providing outsourced services to pharmaceutical, biotechnology, medical device and government and public health organisations. We develop new innovations, drive emerging therapies forward and improve patient lives. With headquarters in Dublin, Ireland, ICON employed approximately 41,150 employees in 109 locations in 53 countries as at March 31, 2023. For further information about ICON, visit: www.iconplc.com.

This press release contains forward-looking statements. These statements are based on management's current expectations and information currently available, including current economic and industry conditions. These statements are not guarantees of future performance or actual results, and actual results, developments and business decisions may differ from those stated in this press release. The forward-looking statements are subject to future events, risks, uncertainties and other factors that could cause actual results to differ materially from those projected in the statements, including, but not limited to, the ability to enter into new contracts, maintain client relationships, manage the opening of new offices and offering of new services, the integration of new business mergers and acquisitions, the impact of COVID-19 on our business, as well as other economic and global market conditions and other risks and uncertainties detailed from time to time in SEC reports filed by ICON, all of which are difficult to predict and some of which are beyond our control. For these reasons, you should not place undue reliance on these forward-looking statements when making investment decisions. The word "expected" and variations of such words and similar expressions are intended to identify forward-looking statements. Forward-looking statements are only as of the date they are made and we do not undertake any obligation to update publicly any forward-looking statement, either as a result of new information, future events or otherwise. More information about the risks and uncertainties relating to these forward-looking statements may be found in SEC reports filed by ICON, including its Form 20-F, F-1, F-4, S-8, F-3 and certain other reports, which are available on the SEC's website at http://www.sec.gov.

ICON/ICLR-G

Contacts

Kate Haven
Vice President Investor Relations
+1888 381 7923