Mark Edward Kelly (born February 21, 1964) is an American politician and a retired astronaut and naval officer. He is the senior United States senator from Arizona, a seat he has held since 2020. He is a member of the Democratic Party.

Kelly flew combat missions during the Gulf War as a naval aviator before being selected as a NASA Space Shuttle pilot in 1996. His identical twin brother, Scott Kelly, also became a NASA astronaut that year. Mark flew his first space mission in 2001 as pilot of STS-108, then piloted STS-121 in 2006, and commanded STS-124 in 2008 and STS-134 (the final mission of Space Shuttle Endeavour) in 2011. In January 2011, Kelly's wife, then-Arizona Representative Gabby Giffords, was shot and nearly killed in an assassination attempt in Arizona. Kelly retired from the Navy and NASA that October. In 2013, Kelly and Giffords founded a nonprofit political action committee, Americans for Responsible Solutions (later merged into Giffords), which campaigned for gun control measures like universal background checks.

Kelly was first elected to the Senate in a 2020 special election triggered by the death of Senator John McCain. He defeated incumbent Republican Martha McSally in the general election, becoming the first Democrat to win the seat since 1962. Kelly was reelected to a full term in 2022.