"I have heard Joe Biden say that he's never discussed business with Hunter. That is false. I have first hand knowledge about this because I directly dealt with the Biden family, including Joe Biden," Tony Bobulinski told reporters in Nashville.
He said his allegations were corroborated by emails, WhatsApp chats, agreements, documents and other evidence. He said he had three phones from the years 2015-2018 with documentation that he planned to turn over to the FBI on Friday.
Bobulinski's remarks to the press were arranged by Trump's campaign shortly before the president was slated to participate in a debate with the former vice president in Tennessee.
The surprise event was reminiscent of a Trump debate with rival Hillary Clinton in 2016 in which he invited women who accused her husband, former President Bill Clinton, of sexual misconduct as guests.
Bobulinski said he had paid his own costs to come to Nashville.
Bobulinski has agreed to cooperate in a Senate investigation of the Bidens. An investigation by the Republican-led Senate Intelligence Committee last month released its findings on the Bidens, presenting no evidence that Joe Biden exerted improper influence over American policy.
Trump and his children have been accused of conflicts of interest of their own since he entered the White House, most involving the family's real estate and hotel businesses in the United States and abroad.