The candidate cited the ability of his opponent, former World Wrestling Entertainment CEO Linda McMahon, to spend an unlimited sum in the race.
"On this basis we have decided, reluctantly and prayerfully, to scale back the campaign," he said in a statement at 9 a.m. "We will release staff to pursue other opportunities and curtail campaign activities. This is not an easy decision or a happy decision. But we believe it is the right decision."
The ex-congressman's announcement likely means his Senate bid is over, but simply suspending his campaign leaves open the possibility of returning to the race if McMahon falters or drops out.
Simmons, who was for some time the front-runner in the GOP field running to replace the retiring Sen. Chris Dodd (D), will step aside to clear the way for his primary opponent McMahon.
But the former wrestling chief has spent over $16 million on her campaign and secured the Connecticut GOP's nomination last week.
The former congressman was seen as national Republicans' top-tier recruit in the race to take on Dodd, whose approval ratings had been flagging in the state. But when Dodd announced his retirement and state Attorney General Richard Blumenthal (D) stepped forward, the dynamics of the race were reshaped.
Smmons said he would now campaign for other candidates, but did not mention McMahon by name.
"While my name will remain on the primary ballot, in the coming months I will devote myself to helping other Republican candidates for public office who I believe will bring to Connecticut and the nation the leadership we need at this most difficult time," he said.
McMahon has been more of a favorite of conservative, Tea Party activists, who may claim another victory following their primary win last Tuesday in Kentucky, when Rand Paul knocked off establishment favorite Trey Grayson in a primary.
The Blumenthal-McMahon race should be off to a dramatic start, nonetheless, especially as McMahon's campaign quickly took credit last week for leaking information to The New York Times that produced a report suggesting Blumenthal had misrepresented his service record during the war in Vietnam. Blumenthal has denied he'd done so deliberately, but still apologized.
This story was first posted at 7:37 a.m and updated at 9:44 a.m.