Romney's closest competitor for the GOP nomination, former Pennsylvania Sen. Rick Santorum, who bowed out of the race last week, has yet to endorse him.
The former Massachusetts governor, who had several campaign stops Tuesday in Pennsylvania, said he was proud to have earned Corbett's support, acknowledging the state would be "crucial" in November.
"Tom has been a wonderful leader for Pennsylvania and shares my values of spurring economic security through scaling back the size of government and promoting pro-growth policies," Romney said.
Corbett offered no formal public endorsement, but appeared with Romney at a fund-raiser in Harrisburg before Romney spoke at the Lancaster County GOP's annual dinner in Lancaster.
In a brief interview as he left the Capitol, Corbett said he had waited for Santorum's decision before making an endorsement.
"Clearly, he's going to be the nominee of the party," Corbett said of Romney. "I'm just giving him the support of my name here and hope to help him here in Pennsylvania."
Corbett had said he would remain neutral as long as other contenders were in the race. Former House Speaker Newt Gingrich and Texas Rep. Ron Paul remain on the GOP ballot in Pennsylvania, but neither has actively campaigned in the state.
At the dinner, Romney told the hundreds of GOP faithful - "There are more Republicans in this room than I had in Massachusetts," he joked - that their state would be pivotal in the general election.
"If we win Pennsylvania, we'll take back the White House and keep America the hope of the earth," he said.
Most of Romney's remarks were aimed at the president, saying Obama had failed to stem job losses, home foreclosures, and deficit increases. Romney said he would return the country to growth.
"There was once a time that America was proud of the fact that we built the interstate highway system and built the Hoover Dam," he said. "Now we can't even build a pipeline. There was a time when we led the world in manufacturing and exports. We now lead the world in lawsuits."
Addressing the dinner after Romney spoke, Gingrich echoed his appeal for Republican support. The last Republican presidential candidate to win Pennsylvania was George H.W. Bush in 1988.
"If we carry Pennsylvania, it is impossible for Barack Obama to win the presidency," Gingrich said, asking voters to consider him on Tuesday.
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Laura Olson and Karen Langley of the Pittsburgh Post-Gazette contributed to this article.