Representative Paul Ryan, a leader in Republican efforts to slash government spending, endorsed presidential candidate Mitt Romney, calling him the party's best chance to beat Democratic President Barack Obama.
Friday's endorsement from Ryan, a Wisconsin conservative, comes four days before his state's primary contest on Tuesday.
"I think he deserves to be the nominee. I think he earned it. He has emerged as the best candidate," Ryan told the Milwaukee Journal Sentinel.
He also called on "conservatives to coalesce around Romney," warning that the Republican party's drawn-out nominating process could be damaging leading up to the November 6 general election, according to the newspaper.
Ryan has been mentioned as a possible vice presidential candidate.
His move follows a string of prominent Republicans who have been falling in line behind the former Massachusetts governor and business executive, including Florida Senator Marco Rubio and former President George H.W. Bush.
In a statement, Romney praised Ryan's work to reform federal spending and thanked him "for all the hard work he has done to help turn around our country and restore it to greatness."
On Thursday, the House passed Ryan's deficit-cutting budget, which calls for tax cuts and cuts to social programs, but the plan is expected to die in the Democratic-led Senate.
"Congressman Ryan has not only thought deeply and creatively about how to bring our extraordinary budget shortfall under control, but he has demonstrated the leadership to bring Americans together to put his bold reforms into practice," said Romney.
Romney is in a drawn-out fight with rival Rick Santorum, a former U.S. senator from Pennsylvania. Other contenders include Representative Ron Paul and former House Speaker Newt Gingrich, who along with Santorum has vowed to compete until the Republican convention in August.