"In order to facilitate a swift and thorough examination of the facts sought by the Senate Intelligence Committee, President Trump will not assert executive privilege regarding James Comey's scheduled testimony," spokeswoman Sarah Huckabee Sanders said in a statement.
Presidents can assert executive privilege to prevent government employees from sharing information.
On Thursday, Comey will speak to an open hearing of the Senate Intelligence Committee followed by a closed session. The hearing is part of the panel's probe into alleged Russian meddling in the 2016 election and any possible ties between the Trump campaign and the Kremlin.
Comey was abruptly fired last month while overseeing the FBI's own investigation of alleged Russian interference. His testimony could potentially be damaging for Trump, but attempting to block Comey could have looked bad for the president, as well.
The former FBI chief will certainly be asked about his reported conversations with Trump and any efforts the president made to interfere with the probe. Robert Mueller, who was FBI director before Comey, is now overseeing the probe as a special counsel.
It is not yet clear how much Comey will say about his conversations with Trump or an alleged memo in which Comey reportedly says the president asked him to back off the investigation into ex-national security advisor Michael Flynn.
People close to Comey say he is eager to speak in public, according to NBC News. He met with Mueller, who cleared him to testify.
It is not clear what Mueller told Comey he could say publicly. Some legal experts have said that, if Mueller is investigating possible obstruction of justice, he may not want Comey to speak in the open about his conversations with Trump, NBC reported.
Trump and the White House have denied any collusion with Russia related to the 2016 election.
— Reuters contributed to this report.
Watch: Comey to testify June 8th