The GOP has seen defeat before, Romney noted, but those stumbles prepared it for bigger victories later on.
"I am sorry that I will not be your president but I will be your co-worker and I will work shoulder to shoulder alongside you," Romney said to applause in National Harbor, Md., just outside the nation's capital. "In the end, we will win for the same reason we won before: because our cause is right and just."
Romney didn't detail what he thought were his mistakes Friday, though he and his wife, Ann, noted in an interview with "Fox News Sunday" recently that they felt the race didn't allow the candidate to show his more open, compassionate side.
"It was not just the campaign's fault," Ann Romney said. "I believe it was the media's fault as well, is that he was not giving being given a fair shake, that people weren't allowed to really see him for who he was."
The former Massachusetts governor, who stepped away from public life after the November election, also took on his own party's post-race pessimism during his CPAC speech but says he "utterly rejects that pessimism."
"We may not have carried the day last November 7th, but we haven't lost the country we love, and we haven't lost our way," Romney said. "We're a nation of invention and of reinventing. My optimism about America wasn't diminished by my campaign; no, it grew. It grew as I came to know more of our fellow Americans."
Republican strategist Ron Bonjean says Romney's appearance shows he wants to keep the door open for a future opportunity in the party.
"Most people want to move forward and not think about Mitt Romney or the 2012 campaign," Bonjean said. "I don't think this speech really changed people's feelings about him either way. But it did send a signal that he's going to stay involved in some capacity, that we'll likely see him again."
Romney's running mate, Rep. Paul Ryan, appeared earlier at the conference, though he didn't mention the former presidential candidate or the failed campaign. Ryan did, however, urge similar action.
"The future's bright," the Wisconsin Republican said. "It's right in front of us. We can do this. We need your help."
Noting that CPAC banned gay groups and gave the longest speaking spots to Sarah Palin and Donald Trump, a spokesman for the progressive American Bridge, said the conservative group may be too busy making more mistakes to learn from anybody else's.
"One look around CPAC is all you need to know conservatives learned all the wrong lessons from November's elections," said spokesman Chris Harris. "Rather than working to broaden their appeal among American voters, conservatives are rapidly moving in the opposite direction."