Former FBI director James Comey will testify before the US Senate Intelligence Committee on 8 June as part of its probe into alleged Russian meddling in the US presidential election and possible collusion with President Donald Trump's campaign.
The committee said Mr Comey would testify in an open session at 10am (3pm Irish time) followed by a closed session.
The former FBI chief was fired by Mr Trump on 9 May.
He is expected to testify on conversations he had with Mr Trump in which the president reportedly asked him to drop an investigation into former White House national security adviser Michael Flynn.
Mr Flynn is one of several Trump associates who are drawing scrutiny in a series of probes about Russia and last year's election.
Russia has repeatedly denied any effort to interfere in the election, and Russian President Vladimir Putin has said some Russians might have acted on their own without their government's involvement.
Mr Trump has denied any collusion between Russia and his campaign and has repeatedly questioned the US intelligence finding that Mr Putin led an operation that included computer hacking, fake news and propaganda intended to swing the election in Mr Trump's favor over Democratic rival Hillary Clinton.
Mr Comey was leading the FBI's probe into the allegations, and his firing sparked a political uproar.
Facing rising pressure, the Justice Department earlier this month named another former Federal Bureau of Investigation chief, Robert Mueller, as a special counsel to investigate the allegations.
A number of congressional committees, in addition to the Senate intelligence panel, are also looking into the matter.
Yesterday, the House of Representatives Intelligence Committee approved subpoenas for Mr Flynn and Mr Trump's personal lawyer, Michael Cohen, in connection with its probe.
In addition, the committee's Republican chairman, Representative Devin Nunes, who had recused himself from the panel's Russia investigation, also approved subpoenas to the CIA, FBI and National Security Agency for information relating to the "unmasking" of the names of Mr Trump campaign advisers inadvertently picked up in top-secret foreign communications intercepts.
Committee aides complained he had acted unilaterally, and the top Democrat on the panel, Representative Adam Schiff, said Mr Nunes' actions amounted to a breach of his recusal decision.
"Commitments to recuse himself have not been fully honored," Mr Schiff told MSNBC.
Mr Trump has backed Mr Nunes' efforts to investigate actions by US security and other officials who had served under previous president Barack Obama.
"The big story is the 'unmasking and surveillance' of people that took place during the Obama Administration," Mr Trump said in a tweet.
The big story is the "unmasking and surveillance" of people that took place during the Obama Administration.— Donald J. Trump (@realDonaldTrump) June 1, 2017