President Biden said on Friday that he would participate in a general-election debate with former President Donald J. Trump, a striking shift after months in which he and his campaign declined to commit to appearing onstage with his Republican rival.

Mr. Biden’s announcement, made in response to a question from the radio host Howard Stern, comes after pressure from television networks and Mr. Trump’s campaign for the president to agree to participate in debates.

When Mr. Stern asked Mr. Biden if he would debate Mr. Trump, the president replied: “I am, somewhere, I don’t know when, but I am happy to debate him.”