In 2018, Mannion ran for the
New York State Senate in the
50th district but narrowly lost to the incumbent, Republican
Bob Antonacci. He ran again in 2020 and won the seat with 52.57% of the vote, defeating Republican Angi Renna. Mannion's 2022 re-election campaign was closely contested. On election night, Republican candidate Rebecca Shiroff led by 396 votes before absentee ballots were counted. A recount ultimately declared Mannion the winner, with a margin of 10 votes, making it the closest race in the 2022 New York State Senate elections. In 2023, Mannion announced his candidacy for
New York's 22nd congressional district in the 2024 election, choosing not to seek re-election to the Senate. In June 2024, three former staffers accused Mannion and his wife of creating a hostile work environment. After an investigation, he was cleared of any wrongdoing.
Committee assignments Mannion was the chairperson of the Committee on Disabilities. He also served as a member of the following committees: • The Committee on Children and Families • The Committee on Civil Service and Pensions • The Committee on Education • The Committee on Environmental Conservation • The Committee on Housing, Construction and Community Development • The Committee on Internet and Technology ==U.S. House of Representatives==