Marco Rubio will run for re-election for his Florida Senate seat, reversing his previous decision to leave Capitol Hill.
Rubio, who ended his White House bid earlier this year, had long insisted that he would be a "private citizen" after his current Senate term expires. But he came under intense pressure from his own party to seek re-election amid concerns that Republicans could lose their majority in the United States Senate.
"Rubio believes we need principled conservatives in the Senate regardless of who is the next president, and now isn't the time to leave public service given all the challenges facing America," an aide told NBC News, noting that the recent mass shooting in Orlando was a major reason for reconsidering his decision.
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With a national profile and a deep fundraising network, Rubio was widely seen as the party's best standard-bearer in the state for what's sure to be an expensive and hard-fought general election race.
The deadline for Rubio to file for re-election is Friday, and the Senate primary will be held August 30.
Rubio indicated last week that he was reconsidering his pledge, suggesting that the massacre at a club in his home state had prompted him to think about his role as a public servant.
He reiterated some of those concerns in an interview with the Miami Herald Wednesday.
"I think that the point that really drove me to change my mind is that as we enter this kind of new chapter in our history here is, there's another role the Senate plays that I think can be really important in the years to come," Rubio told the Herald. "And that's the power given to it in the Constitution to act as a check and balance on the excess of the president. It's even more important given the fact that control of the Senate could very well come down to what happens in the Florida race."
Rubio had also expressed reluctance to enter the race because a close friend, Lt. Gov. Carlos Lopez-Cantera, was already seeking the Senate seat. But Lopez-Cantera told supporters last week that he would drop his efforts if Rubio decided to jump in.
Another GOP challenger, Carlos Beruff, on Wednesday called Rubio "Washington's candidate," saying "This isn't Marco Rubio's seat; this is Florida's seat. The power brokers in Washington think they can control this race."
A Quinnipiac poll out Wednesday showed that Rubio leads Democratic Rep. Patrick Murphy 47 percent to 40 percent. Murphy faces his own primary against Rep. Alan Grayson in August.
In a statement, Murphy said "Marco Rubio abandoned his constituents, and now he's treating them like a consolation prize."