Rep. Edward J. Markey, a Democrat who has toiled for almost 40 years in the House in both the majority and minority, won a promotion to the Senate on Tuesday in a sweeping victory over Gabriel Gomez, a Republican who has never served in elective office.

Markey, 66, succeeds John Kerry, who stepped down this year to become secretary of state, and he will provide a reliable vote for President Barack Obama’s agenda, which seemed to be just what voters wanted.

“The Senate needs to be controlled by Democrats,” said Pam Wechsler, 52, a prosecutor, as she voted Tuesday in the West End of Boston.

With almost all precincts reporting, Markey won 55 percent of the vote to Mr. Gomez’s 45 percent.

“Like you, I’m tired of gridlock,” Markey told a jubilant crowd packed into the ballroom of a hotel here, “but I will never compromise on our principles.”

He said he would lead a green revolution and put steelworkers and ironworkers to work in a new economy.