Democrat William “Mo” Cowan was sworn into the Senate shortly after noon on Thursday, filling the seat that former Massachusetts Sen. John Kerry vacated to become secretary of state.
Flanked by Mr. Kerry and Sen. Elizabeth Warren, the newly-elected Massachusetts Democrat, Mr. Cowan, a longtime aide to Massachusetts Gov. Deval Patrick, took the oath of office from Vice President Joseph R. Biden, swearing to support and defend the Constitution.
“Congratulations, senator, welcome,” Mr. Biden told him, sparking a standing ovation and applause from the family, friends and onlookers looking down from the Senate gallery.
Mr. Patrick tapped Mr. Cowan to the seat on an interim basis last month, and looked on from the floor of the Senate as his friend was sworn in.
Mr. Cowan will serve until a June 25 special election. He has no plans to run for the seat.
Mr. Cowan, a lawyer, is the second black senator in the chamber, joining Republican Sen. Tim Scott of South Carolina, who was the first lawmaker from outside Massachusetts to shake Mr. Cowan’s hand and congratulate him after his swearing-in.