Ed Markey at the Democratic National Convention. (Casey Cunningham/Washington Post)

Rep. Ed Markey (D) plans to run for the Massachusetts Senate seat likely being vacated by Sen. John Kerry (D), President Obama's nominee for secretary of state. 

Markey, 66, has served in the House since 1976 and is the dean of the Massachusetts delegation.  The veteran House member announced his decision in a statement, saying, “There is so much at stake.”

"I refuse to allow the Tea Party-dominated Republican Party to lead us off the fiscal cliff and into recession," Markey said. "I won’t allow the NRA to obstruct an assault weapons ban yet again. I will not sit back and allow oil and coal industry lobbyists to thwart our clean energy future or extremists to restrict women’s rights and health care."

Assuming the Senate confirms Kerry's nomination, there will be a special election for the seat sometime next year. Gov. Deval Patrick (D) will appoint an interim senator who will serve until the winner takes office. In 2009, when Sen. Edward Kennedy (D) died, the governor chose Paul Kirk as a placeholder who did not run in the special election. 

Markey is the first major candidate in the race. Other likely Democratic candidates include state Attorney General Martha Coakley, Reps. Stephen Lynch and Michael Capuano and former Rep. Martin Meehan. On the Republican side, Sen. Scott Brown -- who lost to Democrat Elizabeth Warren in November -- is the overwhelming favorite. A recent poll suggested he would be a formidable candidate. Markey has already started polling residents to test his strengths and weaknesses against Brown.