Former FBI director James Comey has backed down from his legal challenge and agreed to testify in private to the House of Representatives judiciary committee.
He is expected to be questioned over decisions not to prosecute Hillary Clinton over her use of a private email server and the investigation into potential collusion between Russia and Donald Trump's election campaign team.
Mr Comey, who was sacked by the president last year, had tried to quash the subpoena ordering him to answer questions in private.
His lawyer, David Kelley, had accused Republican members of the committee of wanting a closed hearing so they could selectively leak parts of Mr Comey's testimony.
But the former FBI boss has now agreed to Friday's session after the committee said a transcript would be released after 24 hours and that he could speak about it afterwards.
Mr Comey tweeted: "Grateful for a fair hearing from judge. Hard to protect my rights without being in contempt, which I don't believe in.
"So will sit in the dark, but Republicans agree I'm free to talk when done and transcript released in 24 hours. This is the closest I can get to public testimony."
Grateful for a fair hearing from judge. Hard to protect my rights without being in contempt, which I dont believe in. So will sit in the dark, but Republicans agree Im free to talk when done and transcript released in 24 hours. This is the closest I can get to public testimony.
— James Comey (@Comey) December 2, 2018
The agreement was reached a day before lawyers were to appear again in court.
Democrats have said the Republican-led inquiry is an attempt to undermine the inquiry into Russian interference in the 2016 presidential election by Special Counsel Robert Mueller – himself a former FBI director.
Republicans have said the FBI is biased against Mr Trump, citing its decision not to bring criminal charges against his former presidential challenger Hillary Clinton.
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A Justice Department report earlier this year criticised Mr Comey for his handling of the Clinton matter, but said he did not show any bias.
The Republican-led inquiry into the FBI is in a race against time to produce conclusions because it will be shut down as Democrats prepare to take over control of the House of Representatives in January.