(CNN) -- Carte Goodwin will be sworn in Tuesday afternoon as the new senator from West Virginia, temporarily filling the seat formerly held by the late Sen. Robert C. Byrd.
The Democrat is expected to cast a key vote when the U.S. Senate considers extending unemployment benefits later in the day.
A Republican filibuster has prevented Democrats from ending debate on the measure, but with Goodwin's vote and support from two Republicans, Democrats believe they can overcome the GOP maneuver.
Goodwin arrives for work in Washington a day after the West Virginia state legislature approved a plan to hold a special election in November to fill Byrd's old seat.
Gov. Joe Manchin, a Democrat considered a likely candidate for the Senate race, signed the measure after a compromise worked out by state lawmakers won final approval.
The primary election will be August 28 and the vote for Byrd's successor will take place as part of the congressional mid-term election November 2, Manchin said.
Last week, Manchin appointed former aide Goodwin as the interim replacement for Byrd until the special election.