Comey added that he leaked his Trump meeting memos to the media after the president tweeted that he may have tapes of their conversations.
Mr Trump cryptically refused to say whether those private exchanges were taped - a matter at the heart of the conflicting accounts of what passed between them at a time when Mr Comey was leading an FBI investigation into Russia's interference in the presidential election and its ties to the Trump campaign.
"But he testified under oath and I do believe that he's an individual of integrity who would not deliberately lie under oath", Collins told CNN.
The Senate committee sent a request for Comey's memos from the Federal Bureau of Investigation on and a separate request to the White House for any records kept by Trump, on May 17.
Trump abruptly fired Comey as director of the Federal Bureau of Investigation on May 9, later admitting that the Russian Federation probe was on his mind at the time.
He further denied ever asking Mr Comey for his "loyalty", contradicting Mr Comey's detailed sworn testimony about a private dinner the two men had in the White House.
President Trump speaks with reporters during visit by Romanian leader
Trump says he's willing to speak with the special counsel investigating Russian government efforts to meddle in the 2016 US election.
Comey's testimony added fuel to critics' accusations that Trump's actions around the Russian Federation probe might have amounted to obstruction of justice.
Among those brought into his office are Watergate team members Aaron Zebley and James Quarles, as well as the Department of Justice fraud chief Andrew Weissman, who led the Enron investigation.
Comey testified Thursday that Trump asked him to drop an investigation into former national security adviser Michael Flynn and implied Trump may have become the subject of investigation himself for interfering in the FBI's work.
During nearly three hours of statements Thursday before the Senate Intelligence Committee, Comey described himself as "stunned" by Trump's "very disturbing" and "very concerning" behavior towards him.
Trump also seized on Comey's revelation that he had directed a friend to release memos he'd written documenting his conversations with the president to a reporter. Later, he told a reporter, "You're going to be very disappointed when you hear the answer".
"It's a great question", Comey replied.
"It's also true I think from based on what I see as a third party and out of government that there's no basis to say there's no obstruction". The opposite occurred, as the firing created a political firestorm that has stalled Trump's legislative agenda and taken over Washington.