Rep. Ed Markey, D-Mass., will run in the special election to replace Sen. John Kerry, who is expected to be confirmed as secretary of state.
Markey had previously said he would seriously consider a run and put a poll in the field earlier this month testing him in various primary match-ups and against GOP Sen. Scott Brown.
“I have decided to run for the US Senate because this fight is too important,” Markey said in a statement to the Boston Globe. “There is so much at stake.”
The longtime congressman will begin the race with over $3 million in the bank.
Markey is the first candidate to throw his hat into the ring. Earlier in the week, the late Sen. Ted Kennedy's son Edward Kennedy, Jr., and actor Ben Affleck both said they would pass on running. The Democratic field could get crowded, though: Reps. Stephen Lynch and Michael Capuano are both considering bids, among others. Brown has also yet to announce whether he will run again.