House Majority Whip Kevin McCarthy (R-Calif.) is endorsing Mitt Romney to be his party's nominee for president.

"After a long and grueling primary, it is clear that Mitt Romney is the best candidate to face President Obama and fix the mess of his one and only term," said McCarthy in a statement, first reported by The Wall Street Journal.

"Republicans need to unite and work together if we plan to take back the White House and put in place policies that will get our nation back on a path to prosperity by reducing taxes, shrinking government and empowering the private sector. I am proud to support Mitt Romney and urge my fellow Republicans to do the same," he added.

McCarthy's backing provides a boost to the GOP front-runner, who is looking to wrap up support among party leaders in the midst of a protracted primary fight.

"Kevin has been a leading voice in the effort to cut spending, reduce burdensome regulations and make government more accountable to the taxpayers,” said Romney, in a statement released by his campaign. “I share this vision for our country and look forward to working with Kevin on these issues so that we can fix our economy and get the country back on track.”

McCarthy, the third-ranking House Republican, had met Romney last week when the presidential hopeful visited Washington to meet with Capitol Hill leaders. Asked at that time if he would endorse Romney, McCarthy had only responded: "Stay tuned."

McCarthy is the latest prominent Republican to back Romney after the former Massachusetts governor won a pivotal primary in Illinois last Tuesday. 

Last week, Romney secured the endorsement of former Florida Gov. Jeb Bush.

Earlier in March, Romney won the backing of McCarthy's House leadership colleague, Majority Leader Eric CantorEric Ivan Cantor'Release the memo' — let's stop pretending that Democrats are the defenders of the FBI Raúl Labrador, a model for Hispanic politicians reaching higher Eric Cantor: Moore ‘deserves to lose’ MORE (Va.).

The report says that McCarthy will serve as the chairman for Romney's California campaign.

A Los Angeles Times/USC poll released Sunday showed Romney with a sizable lead in California, besting Santorum among registered GOP voters surveyed by 42 percent to 23.

This story was updated at 8:44 a.m.