Gomez, of Cohasset, just southeast of Boston, announced his decision in a statement and a video. He said a formal campaign kickoff would come on Feb. 28, one day after the deadline candidates face to collect the 10,000 signatures needed to qualify for the primary ballot.
The primary will be held on April 30. A special election is scheduled for June 25.
Gomez, who has never held elective office, positioned himself as an outsider, pointing to "a lot of unproductive noise and bickering" in Washington.
"I'm running because I refuse to be cynical about America or America's future. Certainly people will say, 'This can't be fixed,'" Gomez said. "But sending career politicians to do the job would be the same old, same old. Our country is better than its politics."
Gomez, who was born in Los Angeles to parents who moved from Colombia, speaks Spanish and English in the campaign video. In a brief biography, he describes growing up in "a grateful, first-generation American family," which instilled in him a duty to give back to his country, prompting his decision to enter the military.
Gomez also highlighted his experience as a graduate of the U.S. Naval Academy, a Navy aircraft carrier pilot and Navy SEAL. He didn't return phone messages left by The Associated Press.
A campaign aide said Gomez isn't planning to talk to the press before Feb. 28 but has spoken with former Republican Govs. William Weld and Paul Cellucci and former GOP gubernatorial candidate Charles Baker.
"We believe we can win," campaign spokesman Lenny Alcivar said.
Gomez had been trying to line up support ahead of his announcement. On Tuesday his campaign released a statement by former GOP Lt. Gov. Kerry Healey in which she praised him for his "common sense and experience" but stated "primaries are healthy for our party."
Kerry was sworn in as the U.S. secretary of state on Feb. 1, and Democratic Gov. Deval Patrick appointed William "Mo" Cowan to serve as interim senator. Cowan is not running for the seat.
Norfolk state Rep. Daniel Winslow became the first Republican to announce his candidacy last week. Jennie Cassie, a member of the Governor's Council, also is considering entering the race.
Senate Republican Leader Bruce Tarr said he's committed to his job but hasn't ruled out a run for the U.S. Senate and likely would have a decision by Wednesday.
On the Democratic side, U.S. Reps. Edward Markey and Stephen Lynch announced their candidacies. Marisa DeFranco, an immigration attorney, is weighing a run.
Many high-profile Republicans, including Weld and former U.S. Sen. Scott Brown, have decided not to run.
Democrats tried to tie Gomez to failed Republican presidential candidate and former Gov. Mitt Romney. They also faulted Gomez's association with a group that criticized President Barack Obama for taking too much credit for the death of Osama bin Laden. The group, Special Operations OPSEC Education Fund Inc., produced a 22-minute video during last year's presidential election criticizing Obama.
During an interview last year on MSNBC, Gomez credited Obama for giving the green light for the special operation to kill bin Laden but said Obama should have given more credit to the troops. Obama, in announcing bin Laden's death, had credited "the tireless and heroic work of our military and our counterterrorism professionals."
Massachusetts Democratic Party Chairman John Walsh criticized Gomez for "hanging out last year with a secretive group that tried, and failed, to damage the president for his handling of bringing justice to Osama bin Laden." He suggested Gomez was trying to run "the Romney Campaign 2.0."
The 47-year-old Gomez, who left the Navy in 1996 to earn a master's degree from Harvard Business School, has worked for the private equity firm Advent International since 2004. He is married with four children.