"I love Massachusetts and our political process, but I am not running for office," Affleck, 40, posted to Facebook Monday. "We are about to get a great Secretary of State and there are some phenomenal candidates in Massachusetts for his Senate seat. I look forward to an amazing campaign."
Affleck, who grew up in Cambridge, Mass., was the second big-name Democrat to pass Monday on running for Kerry's seat, Politico reported.
Ted Kennedy Jr., the son of the late Sen. Edward Kennedy, had earlier said he did not plan to run.