Former Massachusetts senator Scott Brown (R) will not run for governor in 2014, he announced Wednesday, citing a satisfaction with "fulfilling and exhilarating" opportunities he's pursued in the private sector since leaving office.

"Tonight I announced that I will not be running for Governor of MA in 2014," Brown wrote on his Facebook page. "As I said, I am grateful for your encouragement and support. For the first time in 15 plus years, I have had a Summer to spend with my family. In addition, I have been fortunate to have private sector opportunities that I find fulfilling and exhilarating. These new opportunities have allowed me to grow personally and professionally. I want to continue with that process."

Brown first announced his decision on the "NightSide With Dan Rea" radio program.

Brown scored a major upset in a 2010 special election when he won the seat once held by the late Edward M. Kennedy (D). He was unseated in 2012 by now-Sen. Elizabeth Warren (D).

Since leaving office Brown, has joined a law firm and signed on as a contributor with Fox News. He did not say what his next move would be.

In addition to a run for governor, Brown has left the door open to a run for the Senate in New Hampshire (where he owns a house) and even a run for the White House in 2016. Brown was in the early presidential nominating state of Iowa over the weekend, where he stoked speculation about a White House bid.

Brown's decision will turn the focus on the GOP side of the open governor's race to Charlie Baker, the 2010 nominee who has been considering another bid. Brown said he would support Baker if he runs.

On the Democratic side, Juliette Kayyem, a former Boston Globe columnist and Obama administration homeland security official, announced Wednesday that she is running. She joined a field that includes  Donald M. Berwick, the former administrator for the Centers for Medicare and Medicaid Services; state Treasurer Steven Grossman; state Sen. Daniel A. Wolf, and biotech executive and physician Joseph Avellone.

State Attorney General Martha Coakley (D), a popular figure whom Brown defeated in the 2010 Senate race, is also believed to be considering a run.