He issued a statement saying he has "received a lot of encouragement" to run "and my competitive instincts were leading in the same direction."
"I was not at all certain that a third Senate campaign in less than four years, and the prospect of returning to a Congress even more partisan than the one I left, was really the best way for me to continue in public service at this time," he said.
Brown's announcement came one day after Charlie Baker -- a former state secretary of Administration and Finance and the GOP nominee for governor in 2010 -- said he will not run in the Senate special election. Baker urged Republican former Gov. William Weld to run if Brown decided not to, the Boston Herald reported.
Former Lt. Gov. Kerry Healey is another possible candidate, The Boston Globe said.
So far, the only declared candidates for the special election are U.S. Rep. Stephen Lynch and U.S. Rep. Edward Markey, both Democrats.
A Public Policy Polling survey released this week indicated Markey is a clear favorite to beat Lynch in a primary, with Brown holding a 48-45 edge over Markey in a hypothetical general election match-up.
Gov. Deval Patrick this week named his former chief of staff William "Mo" Cowan to represent Massachusetts in the U.S. Senate until voters decided in a special election who will succeed Kerry.
The primary is scheduled for April 30 and the special election to fill the seat until the 2014 election is set for June 25.