David C. Weiss, who negotiated an ill-fated plea deal with President Biden’s son Hunter, is set to defend his investigation before the House Judiciary Committee on Tuesday, the first time a special counsel has agreed to field queries from Congress before concluding an inquiry.

Mr. Weiss, the Trump-appointed U.S. attorney in Delaware, plans to use the interview to counter claims that he brokered a sweetheart deal with Hunter Biden under pressure from the White House. He is also set to dispute a whistle-blower’s allegation that he once complained that he had not been given full authority to prosecute Hunter Biden on tax charges.

The special counsel “is prepared to take this unprecedented step of testifying before the conclusion of his investigation to make clear that he’s had and continues to have full authority over his investigation and to bring charges in any jurisdiction,” according to his spokesman, Wyn Hornbuckle.

House Republicans have made their charges of favorable treatment for Mr. Biden a key piece of their sputtering efforts to impeach the president. Their theories have remained unsupported — and often directly contradicted — by the evidence.

Mr. Weiss is not expected to discuss the federal investigation into Mr. Biden’s lucrative foreign business dealings, or his recent indictment of Mr. Biden on three charges related to his illegal purchase of a handgun in 2018, when he was addicted to drugs and alcohol, Mr. Hornbuckle said.

“Consistent with department policy and the law, he will be unable to address the specifics of his investigation,” Mr. Hornbuckle said.