Scott Brown, a little-known Republican state senator, rode an old pickup truck and a growing sense of unease among independent voters to an extraordinary upset Tuesday night when he was elected to fill the Senate seat that was long held by Edward M. Kennedy in the overwhelmingly Democratic state of Massachusetts.
By a decisive margin, Mr. Brown defeated Martha Coakley, the state’s attorney general, who had been considered a prohibitive favorite to win just over a month ago after she easily won the Democratic primary.
With all precincts counted, Mr. Brown had 52 percent of the vote to Ms. Coakley’s 47 percent.
“Tonight the independent voice of Massachusetts has spoken,” Mr. Brown told his cheering supporters in a victory speech, standing in front of a backdrop that said “The People’s Seat.”