Mitt Romney has tapped Wisconsin Rep. Paul Ryan to be his running mate, The Associated Press reports.

A Republican with knowledge of the development confirmed the selection to the AP, hours ahead of an official announcement at 8:45 a.m. during a campaign stop Saturday morning in Norfolk, Va. Romney will then launch his "The Romney Plan For A Stronger Middle Class" bus tour.

The selection comes roughly two weeks before the start of the Republican National Convention in Tampa, and gives Romney plenty of space to rally the party behind his pick before the official nomination.

The announcement comes as some polls, including a recent Fox News survey, show the Republican presidential candidate losing some ground to President Obama.

Several Republicans were thought to be on the short list. A GOP source confirmed to Fox News that one of them, Ohio Senator Rob Portman, was informed by Romney himself that he was not the pick.

Ryan, already considered a rising star in the Republican Party, is chairman of the House Budget Committee. He’s been in Congress since 1999 and is best known this session for his controversial budget plan that includes an overhaul of Medicare.

Democrats have persistently tried to vilify that plan as a scheme to “end Medicare as we know it.”

But Ryan, a bookish but telegenic lawmaker, has stuck by his proposal as the solution to an ever-growing deficit inflamed by out-of-control entitlement spending.

Ryan has made fiscal discipline the touchstone of his tenure on the budget committee. As a running mate, Ryan could focus on plans for balancing the government’s books while on the stump, as Romney focuses on his jobs-creation proposals.