The president will appear at a Sept. 20 fundraising event in Philadelphia, his first appearance with Sestak as a Senate candidate.
"Joe is honored that the president will do an event with him while he is in Pennsylvania," the campaign said in a statement. "They may have had their differences in the past but they agree on the importance of having pragmatic leader like Joe, who will fight for Pennsylvania's working families, in the Senate."
Sestak, a second-term congressman from the Philadelphia suburbs and a retired Navy admiral, appears to be trailing in the polls against Republican Pat Toomey, a businessman, former congressman and ex-president of the Washington-based free-market advocacy group Club for Growth.
A statewide survey last week by Franklin & Marshall College showed Toomey ahead, with 40 percent of likely voters to Sestak's 31 percent. The same poll showed that 63 percent of people believe Obama is doing a fair or poor job as president.
The election is Nov. 2.
In the primary, Sestak defeated Obama-backed Sen. Arlen Specter, a longtime moderate Republican who switched parties rather than face Toomey in a GOP primary.
Since then, outside groups have been airing a string of negative television commercials that paint the candidates as irresponsible and extreme.
With the economy and the national debt in the front of voters' minds, Sestak and Toomey both have outlined why they think the other is to blame.
Republicans are linking the weak economy to Sestak and his support for the policies of the Obama administration.
"With more than 80,000 jobs lost in the state since passage of the Democrats' stimulus, the president's visit will only remind voters of Joe Sestak's unwavering support for his failed economic agenda," Republican Party spokesman Parish Braden said in a statement Friday.