Sen. Max Baucus, the Montana Democratic chairman of the powerful Senate Finance Committee, will not seek re-election to a seventh term next year, a party aide said Tuesday.
Baucus, 71, first elected to the Senate in 1978, will become the seventh senator—five Democrats and two Republicans—to announce plans to retire at the end of next year.
Baucus' office had no immediate comment on his plans.
Democrats currently have a 55-45 majority in the Senate. Former Montana Democratic Gov. Brian Schweitzer is a leading contender to run for Baucus' seat.
Baucus' Senate Finance Committee is working to revamp the U.S. tax code. He played a key role in President Barack Obama's landmark overhaul of the U.S. health care system, which was signed into law in 2010.
Baucus' decision to not seek re-election did not come as a surprise to many fellow Democrats who knew that the remarried senator was considering retirement, aides said.
If Democrats retain the Senate in next year's election, Democratic Sen. Ron Wyden of Oregon is next in line in party seniority to replace Baucus as Finance Committee chair.