U.S. Senator John McCain on Wednesday endorsed former Massachusetts Governor Mitt Romney for the Republican presidential nomination.

Republican presidential candidate, former Massachusetts Gov. Mitt Romney and his wife Ann embrace at the Hotel Fort Des Moines on the night of the Iowa Caucuses January 3, 2012 in Des Moines, Iowa. [Xinhua]

"I am really here for one reason and one reason only, and that is to make sure that Mitt Romney is the next president of the United States," McCain told a crowd in Manchester, New Hampshire. "New Hampshire is the state that will catapult him on to victory in a very short period of time."

The senator won the New Hampshire primary in 2008, defeating rivals including Romney and former Arkansas Governor Mike Huckabee, among others. He won the GOP nomination but was eventually defeated by Barack Obama, then the Democratic nominee and now the president.

The endorsement came a day after Romney beat former Pennsylvania Senator Rick Santorum by only eight votes in Iowa, the first state to vote on who will be the Republican Party's presidential candidate.

The endorsement will help Romney solidify his position in the upcoming New Hampshire primary on Jan. 10. Romney has been consistently running strong in the Granite state, with double-digit lead over his rivals.

Forty-seven percent of Republican voters support Romney as the party's nominee, followed by House Representative Ron Paul of Texas at 17 percent, according to a CNN poll released Tuesday night. Former Utah Governor Jon Huntsman ranks third with 13 percent of the vote.

Romney has been the favorite of the Republican establishment with a long list of endorsement. But it was dismissed by his rivals as simply a proof of his popularity among Washington insiders.