Peter Francis Welch (born May 2, 1947) is an American lawyer and politician serving as the junior United States senator from Vermont since 2023. A member of the Democratic Party, he served as a U.S. representative for Vermont's at-large congressional district from 2007 to 2023. He has been a major figure in Vermont politics for over four decades, and is only the second Democrat to be elected a senator from the state.

Welch served in the Vermont Senate from 1981 to 1989, including terms as minority leader. He was the Senate's president pro tempore from 1985 to 1989, the first Democrat to hold the position. In 1988, he gave up his seat to run for the United States House of Representatives and lost the Democratic primary to Paul N. Poirier. He was the Democratic nominee for governor of Vermont in 1990, losing the general election to Republican Richard A. Snelling.

Welch continued to practice law and returned to politics in 2001, when he was appointed to fill a vacancy in the Vermont Senate. He was re-elected in 2002 and 2004 and served as Senate president from 2003 to 2007. In 2006, Welch was elected to the U.S. House of Representatives, succeeding Bernie Sanders, who was elected to the United States Senate. In November 2021, Welch announced his candidacy for the Democratic nomination in the 2022 United States Senate election in Vermont to succeed retiring Senator Patrick Leahy. On August 9, 2022, he won the Democratic primary. On November 8, 2022, Welch won the general election, defeating Republican nominee Gerald Malloy. Elected at age 75, he is the oldest person to become a freshman senator, a record previously held by Frederick H. Gillett.