Stefanowski was the Republican Party nominee for Governor of Connecticut in 2018 and 2022, losing both times to Democrat Ned Lamont.

He then served as chief financial officer of UBS, where he restructured the Investment Bank to meet Basel III regulatory requirements.

[11][12] Stefanowski's tax-cut proposals were backed by Republican economic commentators Arthur Laffer and Larry Kudlow.

[14][15] His campaign ran television commercials, beginning in January 2018, in the Hartford-New Haven and New York media markets; his ads criticized Democratic governor Dannel P. Malloy, promoting Stefanowski's economic proposals (co-authored with Laffer)[16] and criticizing Malloy's acceptance of publicly funded elections.

[18] He received endorsements from former Republican competitor Peter Lumaj, state representative Noreen Kokoruda, state senator Len Suzio, former U.S. Comptroller General David M. Walker, Middletown Planning and Zoning Commissioner Tyrell Brown, Middletown Board of Education member Edward Ford, Jr., and Shelton Mayor Mark Lauretti.

[26][27][28][29] In August 2018 primary, Stefanowski won the Republican nomination, receiving 29.4% of the vote, surpassing Boughton (21.3%), David Stemerman (18.3%), Tim Herbst (17.6%), and Steve Obsitnik (13.4%).

[33] On November 8, 2022, Stefanowski lost the general election to incumbent governor Ned Lamont in a rematch of their 2018 race, this time with a 13% margin.