Ex-FBI chief James Comey will tell Congress on Thursday President Donald Trump wanted a “patronage relationship” and asked for his “loyalty”.
According to his opening statement, Mr Comey will also testify the president asked him to drop an inquiry into fired National Security Adviser Mike Flynn.
He says Mr Trump called the Russian probe “a cloud” over him.
Mr Comey also says he had told Mr Trump three times he was not under scrutiny, confirming the president’s account.
Reacting to the prepared testimony on Wednesday evening, Mr Trump’s private legal counsel on the Russia inquiry, Marc Kasowitz, said the president was “pleased” Mr Comey had confirmed he was not in investigators’ crosshairs.
“The president feels completely and totally vindicated,” said the attorney.
Two national security officials, NSA Director Mike Rogers and Director of National Intelligence Dan Coats, earlier testified to senators that they never felt pressured by the White House to do anything illegal.
But in Thursday’s Senate Intelligence Committee hearing, Mr Comey will detail how Mr Trump made him uncomfortable during a series of encounters leading up to the FBI director’s firing on 9 May.
It is one of several congressional panels that, along with the Justice Department, is investigating US intelligence assessments that Russian hackers meddled in last November’s presidential election in an effort to help Mr Trump beat Democratic candidate Hillary Clinton.
The inquiries are also investigating whether any Trump campaign officials colluded with the alleged Kremlin plot, which Moscow has repeatedly denied.
According to seven pages of prepared testimony, Mr Comey will say his first meeting with the president occurred on 6 January in a conference room at Trump Tower, where Mr Comey briefed him alone on “salacious and unverified” allegations about him.
A dossier compiled by a former British intelligence official had claimed the Russian security services possessed compromising material on Mr Trump, including that he had been recorded consorting with prostitutes at a Moscow hotel.
Mr Comey’s statement says the president “expressed his disgust for the allegations and strongly denied them” during a subsequent meeting.
That denial came in a one-to-one dinner on 27 January at the White House, Mr Comey will say, adding that he had a “very awkward conversation” with the president that evening.