Gregory Richard Gianforte (/ˌdʒiːənˈfɔːrteɪ/ JEE-ən-FOR-tay; born April 17, 1961) is an American politician, businessman, and software engineer serving as the 25th governor of Montana since 2021. A member of the Republican Party, Gianforte served as the U.S. representative for Montana's at-large congressional district from 2017 to 2021.

In 1997, Gianforte and his wife, Susan, co-founded RightNow Technologies, a customer relationship management software company. The company went public in 2004; by that time, it employed over 1,000 workers. RightNow Technologies was acquired by Oracle Corporation for $1.5 billion in 2011.

In 2016, Gianforte ran for governor of Montana as the Republican nominee, losing to incumbent governor Steve Bullock. In May 2017, Gianforte defeated Democratic nominee Rob Quist in a special election for Montana's at-large congressional seat to fill a vacancy created by the appointment of Ryan Zinke as U.S. Secretary of the Interior. Gianforte was convicted of misdemeanor assault in state court in June 2017 stemming from an assault on The Guardian political reporter Ben Jacobs in May 2017. He was fined and sentenced to community service and anger management therapy. Gianforte was reelected in 2018, defeating Democratic nominee Kathleen Williams.

Gianforte did not seek reelection to the House of Representatives in 2020 and instead was a candidate in the 2020 Montana gubernatorial election. In the November general election, he defeated incumbent lieutenant governor Mike Cooney. He is the first Republican to serve as governor of Montana since Judy Martz left office in 2005. He defeated Democrat Ryan Busse in the 2024 Montana gubernatorial election, becoming the first Republican to be elected governor of Montana twice since Marc Racicot in 1996.

Gregory Richard Gianforte was born on April 17, 1961, in San Diego, California. He is the oldest son of Frank Richard Gianforte, who had a career as an aerospace engineer and, later, as a landlord. His mother, Dale Douglass, worked for General Dynamics in San Diego, and later was a school math teacher. Gianforte is of Italian, English, and Scottish ancestry. He has two younger brothers, Douglass and Michael. After the age of three, Gianforte was raised in the Valley Forge and King of Prussia suburbs northwest of Philadelphia, Pennsylvania, including Wayne, an affluent unincorporated township community that extends into Montgomery, Chester, and Delaware Counties.

During his high school years in the 1970s, Gianforte started a software business. He attended Upper Merion Area High School in King of Prussia, Pennsylvania, where he was elected class president during his junior and senior years. Gianforte was also captain of his school football team, where he played left offensive guard. He graduated from high school in 1979.

Gianforte graduated in 1983 from his father's alma mater, Stevens Institute of Technology, with a BE in electrical engineering and a master's degree in computer science. He directed a computer lab with 12 programmers. He was a member of the Delta Tau Delta men's fraternity, and enjoyed playing squash.

Gianforte began his career in 1983 at Bell Laboratories, working in product acquisition. Frustrated by the bureaucratic corporate hierarchy at Bell Labs, Gianforte departed to co-found Brightwork Development Inc., a developer of server-based LAN management software for the banking industry, which was based in Tinton Falls, New Jersey. He and his partners sold the company to McAfee Associates for $10 million in 1994. Gianforte then began working for McAfee as head of North American sales. In 1995, he moved to Bozeman, Montana.