Robert K. Hur, the special counsel who investigated President Biden, on Tuesday fiercely defended the disparaging assessment of the president’s mental state included in his final report — and his decision not to charge Mr. Biden with a crime.

Mr. Hur, appearing before the House Judiciary Committee to answer questions about his polarizing 345-page report, cast himself as an impartial arbiter. He said he had expressed concerns about Mr. Biden’s memory because he needed to justify not bringing a case against Mr. Biden after some evidence showed that the president had willfully retained sensitive material from his vice presidency.

“I resolved to do the work as I did all my work for the department: fairly, thoroughly and professionally,” he said in his opening statement.

Mr. Hur, a registered Republican who has been slammed by Mr. Biden’s allies for including his politically damaging assessment of Mr. Biden’s memory, showed little emotion during the hearing, but reacted angrily when a Democrat suggested he had “smeared” the president to bolster Mr. Trump.

“Partisan politics played no part whatsoever in my work,” said Mr. Hur, 51, a former Trump Justice Department official whose appointment was lauded by some Democrats who praised his work as a prosecutor in Maryland.

About an hour before Mr. Hur testified, Democrats on the congressional panel released a lightly redacted transcript of the five-hour interview Mr. Hur and his team conducted with Mr. Biden. It offered a more nuanced portrayal than the special counsel’s damning description of the 81-year-old president as “a sympathetic, well-meaning, elderly man with a poor memory.”