Tagg Romney played a high-profile role in his father's unsuccessful presidential campaign last year, acting as a top surrogate and behind-the-scenes adviser and strategist.
He told the Boston Herald in a statement GOP Republican candidate in a race to fill former Sen. John Kerry's seat after Kerry was confirmed secretary of state last week.
"I have been humbled by the outreach I received this weekend encouraging me to become a candidate for the U.S. Senate," Romney told the Herald in an email. "I love my home state and admit it would be an honor to represent the citizens of our great commonwealth. However, I am currently committed to my business and to spending as much time as I can with my wife and children. 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 U.S. senator."
Former Sen. Scott Brown announced Friday he would not run again after being defeated by Democrat Elizabeth Warren in November. Brown won a special election in 2009 following the death of Edward Kennedy, shocking Democrats in the solidly liberal Bay State.
Other high-profile Massachusetts Republicans have also said they do not plan to run, Politico said. They include former Gov. William Weld and former state Senate Minority Leader Richard Tisei.
Two Democrats have announced candidacies. Reps. Ed Markey and Stephen Lynch will face off in an April 30 primary. The special election will be held June 25.