Facing a procession of questions from the Senate Intelligence Committee, Comey provided a great deal of insight into his, and Trump's, actions throughout the highly anticipated hearing.
Here are the key moments from James Comey's testimony:
Comey fights back, calls Trump and White House liars
In his opening remarks, Comey described the immediate aftermath of his firing, explaining his belief that the White House engaged in a campaign to damage his and the bureau's reputation.
"Although the law requires no reason at all to fire an FBI director, the administration then chose to defame me and more importantly the FBI by saying that the organization was in disarray, that it was poorly led, that the workforce had lost confidence in its leader," said Comey.
"Those were lies plain and simple," he continued. "And I am so sorry that the FBI workforce had to hear them and I am so sorry that the American people were told them. I worked every day at the FBI to help make that great organization better."
Comey says he was fired to 'change' Russia investigation
After Comey's dismissal, the White House and Trump offered conflicting explanations for why the firing took place -- from Comey's actions during the Clinton email investigation to his management of the bureau and the Russia probe. The former director said he wasn't certain why he was fired but would believe Trump after the president disclosed he was thinking about Russia when he made the decision.
"I don't know for sure. I know I was fired. Again, I take the president's words. I know I was fired because of something about the way I was conducting the Russia investigation was in some way putting pressure on him, in some way irritating him, and he decided to fire me because of that," said Comey.
"It's my judgment that I was fired because of the Russia investigation. I was fired in some way to change or the endeavor was to change the way the Russia investigation was being conducted. That is a very big deal," he added. "Not just because it involves me. The nature of the FBI and the nature of its work requires that it not be the subject of political consideration."
In an earlier moment, Comey was asked to consider what might have happened under a hypothetical President Hillary Clinton.
"I might have been [fired]. I don't know," said Comey. "Look, I've said before that was an extraordinarily difficult and painful time. I think I did what I had to do [in sharing information about the email investigation]. I knew it was going to be very bad for me personally and the consequences of that might have been, if Hillary Clinton was elected, I might have been terminated. I don't know. I really don't."
Trump not personally under investigation, Comey sought to assure him on dossier
The salacious, unverified dossier produced by former British spy Christopher Steele brought out a "strong and defensive reaction" from Trump according to Comey, upon which the director explained to the president that he was not personally under investigation.
"It was important for me to assure him we were not personally investigating him and the context then was narrower, focused on what I just talked to him about," said Comey.
"I was worried very much of being in kind of a J. Edgar Hoover-type situation," said Comey, referring to the bureau's powerful founding director who was known to compile damaging information about Washington elites. "I don't want him thinking I was briefing him on this to sort of hang it over him in some way."
Comey added that he volunteered the information to Trump and that as of his dismissal on May 9, the president's status had not changed.
'Lordy, I hope there are tapes'
In a moment of candor, Comey responded to a question from Sen. Dianne Feinstein, D-California, about why he didn't tell Trump that the nature of their conversations were bordering on being inappropriate.
"That's a great question. Maybe if I were stronger, I would have," said Comey. "I was so stunned by the conversation that I just took it in and the only thing I could think to say, because I was playing in my mind to remember every word he said, I was playing in my mind, what should my response be."
He added that, as a result, he chose his words "carefully," so as not to cross any lines and referred to a tweet of Trump's suggesting their conversations were taped, welcoming their release.
"I've seen the tweet about tapes," said Comey. "Lordy, I hope there are tapes."
Comey took Trump's direction as an order
In his line of questioning, Sen. Jim Risch, R-Idaho, honed in on whether Trump might have obstructed justice when he requested that Comey drop the Flynn investigation. He began by confirming what exactly Trump said to Comey.
"'I hope can you see your way clear to letting this go to letting Flynn go. He is a good guy. I hope you can let this go,'" said Risch, quoting Trump from Comey's written testimony. "Is that correct?"
Both Risch and Comey agreed that the request did not constitute an "order," but Comey noted there was nuance to the situation and that while the words didn't provide direction, he believed it was what Trump sought from him.
"He's the president of the United States, with me alone, saying 'I hope this.' I took it as, 'This is what he wants me to do,'" said Comey. "I didn't obey that. That's the way I took it."
Comey asked friend to share memo contents with press to prompt special counsel
The contemporaneous memos written by Comey detailing his conversations with Trump were major news throughout May, following Comey's firing. He disclosed Thursday how they became public.
"My judgment was I need to get [the memos] out into the public square," said Comey. "So I asked a friend of mine to share the content of the memos with a reporter. I didn't do it myself for a variety of reasons, but I asked him to because I thought that might prompt the appointment of a special counsel."
Comey later added that the crush of reporters outside his home -- which he characterized as "seagulls at the beach" -- drove his decision to ask a friend (Columbia Law School Professor Daniel Richman) to go to the press.
'The Russians interfered in our election'
On a number of occasions, Comey reiterated the findings of the U.S. intelligence community earlier in the year -- that Russia attempted to influence the outcome of the election.
"There should be no fuzz on this whatsoever. The Russians interfered in our election during the 2016 cycle," said Comey. "They did with purpose, they did with sophistication. They did it with overwhelming technical efforts and it was an active measures campaign driven from the top of that government.
"There is no doubt on that. It is a high competence judgment of the entire intelligence community and the members of this committee have seen the intelligence," he continued. "It's not a close call. That happened. That's about as 'unfake' as you can possibly get and it is very, very serious, which is why it's so refreshing to see a bipartisan focus on that. Because this is about America, not any particular party."
Comey says Loretta Lynch asked him not to call Clinton email probe an 'investigation'
Describing the circumstances that led to his public announcements about the status of the investigation into Clinton's use of a private email server while secretary of state, Comey pointed to his concern with an impromptu June 2016 meeting between former President Bill Clinton and then-Attorney General Loretta Lynch.
Not only did the former director indicate that he wanted to maintain the FBI's independence, but said he was also troubled by Lynch's comments about the inquiry.
"At one point, the attorney general directed me not to call it an 'investigation,' but instead to call it a 'matter,' which confused me and concerned me," said Comey. "But that was one of the bricks in the load that led me to conclude I have to step away from the Department [of Justice] if we were to close this case credibly."
Comey concerned Trump 'might lie'
The committee's vice chairman, Sen. Mark Warner, D-Virginia, asked Comey why he felt compelled to take contemporaneous notes about his meetings with Trump when he didn't with other presidents.
"First, I was alone with the president of the United States -- the president-elect, soon to be president," said Comey. "The subject matter -- I was talking about matters that touch on the FBI's core responsibility and that relate to the president-elect, personally.
"Then, the nature of the person," he added. "I was honestly concerned he might lie about the nature of our meeting, so I thought it really important to document."
Was there collusion between Trump and Russia?
Comey sought not to provide his own opinion on whether there was collusion in the election-meddling efforts, explaining again that while he led the FBI, the president wasn't under suspicion. He left the matter open for the ongoing investigation to answer, however.
"Do you believe Donald Trump concluded with Russia? asked Sen. Tom Cotton, R-Arkansas.
"That's a question I don't think I should answer in an open setting," said Comey. "When I left, we did not have an investigation focused on President Trump. But that's a question that will be answered by the investigation, I think."