In his preparation to face Republican vice presidential candidate and House Budget Committee Chairman Ryan, Vice President Biden will rehearse by debating the committee's top Democrat, Rep. Chris Van Hollen, a source with knowledge of the debate preparations told CNN.
The decision signals the central role budget and entitlement issues may play in the debate and fall election, and follows the central role those issues have played since Paul was announced as presumptive Republican presidential nominee Mitt Romney's No. 2 nearly a week ago.
It also puts Biden opposite someone who knows well Ryan and his fiscal prowess.
Van Hollen's role was first reported by The New York Times.
The Maryland congressman has accused Ryan on an Obama campaign conference call of supporting giving "windfalls to the private insurance companies" at the expense of taxpayers and the solvency of Medicare.
The two men participated in their first mock debate session last week.
Olson is one of the fiercest legal minds of his generation and successfully argued for George W. Bush in the landmark 2000 Supreme Court case Bush v. Gore.
He has become a staunch advocate for same-sex marriage in recent years and has argued in federal court against California's Prop. 8, which banned gay marriage. That earned him the enmity of some conservatives who saw him as a sellout.
Olson served as solicitor general under President George W. Bush and has argued 58 cases before the Supreme Court, winning three quarters of those cases.
"Joe Biden has been in elected office for more than 40 years," said Brendan Buck, a spokesman for Ryan. "There are few people in politics with more experience debating the issues than Joe Biden, so we are taking this process seriously. Mr. Olson is one of the most skilled, intelligent and successful litigators in America -- just the kind of opponent needed to prepare the congressman for Mr. Biden."
The vice presidential debate is slated to take place on Thursday, October 11th at Centre College in Danville, Kentucky.