Massachusetts Gov. Deval Patrick has named former party chairman Paul Kirk to fill the seat of the late Sen. Edward Kennedy.
The governor announced his choice at a news conference at the Statehouse on Thursday.
Patrick said the issues before Congress are "too important to Massachusetts for us to be one voice short."
Kirk will serve in the interim until voters pick a replacement in a Jan. 19 special election.
Kirk is a Kennedy family friend who served on the late senator's staff for eight years and is the chairman of the JFK Library Foundation.
Both Ted Kennedy's widow, Vicki Kennedy and his son Edward Kennedy, Jr. had urged Patrick to pick Kirk.
Kirk's appointment will also give President Barack Obama the critical 60th U.S. Senate vote to pass a health care overhaul.
Kennedy died in August of brain cancer.