The Boston Herald first reported that Tagg, son of former GOP presidential nominee Mitt Romney, was considering entering the special election to replace Secretary of State John Kerry (D).
"The timing is not right for me, but I am hopeful that the people of Massachusetts will select someone of great integrity, vision, and compassion as our next US Senator," he said.
His decision not to enter the race further whittles down a narrowing field of possible candidates, since Scott Brown announced on Friday he would not be joining the race. Long considered the most viable and probable candidate for a run, Brown's exit has left the Massachusetts Republican Party scrambling to find a candidate to mount a challenge in what was looking to be a tough race from the outset.
A number of other prominent candidates, including former GOP Gov. Bill Weld and former GOP House contender Richard Tisei, have already ruled out runs.
Tagg Romney was one of the few remaining candidates with high name recognition, but Republicans in the state privately expressed skepticism at his possible candidacy, noting that his father lost in 2012 by more than 20 points, and left the governor's office with a 34 percent approval rating.
Now, attention falls on a handful of state legislators and a local businessman as Republicans begin to game out a field devoid of Brown.