Romney, campaigns in Irmo, S.C. on Wednesday. (Charles Dharapak/AP)

McDonnell (R) will speak about the endorsement on a series of national TV talk shows and then fly to South Carolina to campaign for Romney at a Charleston rally.

The endorsement of Romney by McDonnell, one of the most popular governors in America and a possible vice presidential candidate, comes a day before the South Carolina primary.

McDonnell has said for months that he preferred a governor or former governor. Romney became the last governor in the race after Texas Gov. Rick Perry, a friend of McDonnell’s, dropped out.

Romney, the national front-runner for the Republican presidential nomination, has been in Virginia several times this cycle for fundraisers and to campaign for legislative candidates last year.

Only Romney and Rep. Ron Paul (Tex.) will appear on the Virginia primary ballot March 6. The other candidates — former House speaker Newt Gingrich and former senator Rick Santorum (Pa.) — did not qualify.

Romney has already announced a leadership team in Virginia, led by Lt. Gov. Bill Bolling. He also has support from former governor James Gilmore and several legislators. Attorney General Ken Cuccinelli has stayed out of the race.

Update, 7:30 a.m. Romney’s campaign announced the endorsement in a statement.

“Governor McDonnell’s leadership in Virginia is an example for the rest of the nation,” Romney said. “Governor McDonnell has used the conservative principles of keeping taxes and spending low and creating a fair regulatory climate to make Virginia a top destination for job creators. These same principles can be used in Washington to fix our economy and make government accountable to the taxpayers. I am proud to have his support and look forward to working with Governor McDonnell.”

McDonnell writes in a statement that a governor would make the best president because they have to find solutions and get results for their citizens.

“Mitt Romney has been an effective leader his entire life, in business, the Olympics and as governor,’’ McDonnell said in a statement. “President Obama’s lack of leadership experience is now clear – he has failed to turn around the economy and end the gridlock in Washington. Mitt Romney used his leadership ability in a politically difficult environment to balance the budget every year, cut spending and taxes, and create jobs. He is a results-oriented conservative. This is the type of record that conservatives like me are honored to support – we need a leader like Mitt Romney in the White House to enact effective change that will put our country back on the right path and Americans back to work.”

View Photo Gallery: The GOP presidential contenders.