The announcement at an Arlington, Va., news conference came one week after Gingrich lost five more contests to former Massachusetts Gov. Mitt Romney. Since the caucus-primary season began, Gingrich has won only two contests: South Carolina and his home state of Georgia, garnering 137 of the 1,141 delegates needed to secure the nomination.
"Today I am suspending the campaign," Gingrich said. "But suspending the campaign does not mean suspending citizenship. Callista and I are committed to being active citizens. Now we're going to put down the roles of candidate and candidate's spouse and take up the role of active citizens."
Gingrich gave lukewarm support to Romney, saying compared with President Obama, Romney is the conservative choice.
"This is not a choice between Mitt Romney and Ronald Reagan," Gingrich said.
In an interview with USA Today on the eve of his announcement, Gingrich said he would support Romney's candidacy and is ready to stump for him.
Gingrich said he would officially endorse Romney's candidacy when the two men make a joint appearance soon, USA Today reported Wednesday.
In a phone interview Tuesday, Gingrich said he doesn't regret his decision to run for president but has "regrets about not being smarter about how to run."
With "more discipline and more courage to be more outside the mainstream, it might have worked better," he said.
Gingrich's campaign ends in the red. In a March 31 report to the Federal Election Commission, the campaign said it owed $4.3 million. A campaign official said about $500,000 has been paid since the report.
Gingrich posted a message to supporters on YouTube Tuesday, thanking voters and volunteers and warning re-electing Obama "would be a genuine disaster."