© Kevin Lamarque / Reuters
"The FBI is one of our Nation's most cherished and respected institutions and today will mark a new beginning for our crown jewel of law enforcement," said President Trump.
"While I greatly appreciate you informing me, on three separate occasions, that I am not under investigation, I nevertheless concur with the judgment of the Department of Justice that you are not able to effectively lead the Bureau," Trump told Comey in a letter.
The letter announcing the termination was hand-delivered to FBI headquarters by Keith Schiller, a Trump security aide, according to several reports citing a White House official.
A search for a new permanent FBI Director will begin immediately.
The firing of Comey comes days after he testified to Congress on investigations into alleged Russian meddling in the 2016 US election.
Earlier Tuesday, the FBI wrote to Congress to correct misstatements Comey made regarding a separate investigation into Hillary Clinton's mishandling of classified information.
Comey had testified that top Clinton aide Huma Abedin had forwarded "hundreds and thousands" of emails to her husband, former New York Congressman Anthony Weiner, the FBI clarified that most of those emails had been on his laptop via backup devices, while only a few had been the result of forwarded emails, the Associated Press reported.
Comey reportedly heard of the news from TV reports while addressing FBI employees at the Los Angeles field office, according to New York Times reporter Michael Schmidt and New York Magazine reporter Yashar Ali. Comey was due to speak at an FBI recruiting event in Hollywood Tuesday evening, but that speech has been canceled.
In a memorandum to Sessions from Rosenstein, the deputy attorney general wrote that over the past year, "the FBI's reputation and credibility have suffered substantial damage, and it has affected the entire Department of Justice."
Rosenstein wrote that he could not defend "the Director's handling of the conclusion of the investigation of Secretary Clinton's emails, and I do not understand his refusal to accept the nearly universal judgment that he was mistaken."
"Almost everyone agrees that the Director made serious mistakes; it is one of the few issues that unites people of diverse perspectives," the deputy attorney general added in the memo to Attorney General Sessions.
Rosenstein cited the July 5, 2016 announcement by Comey that the probe into Clinton had concluded without prosecution, which Rosenstein said was not the function of an FBI director, but rather the DOJ.
Rosenstein called Comey's press conference "a textbook example of what federal prosecutors and agents are taught not to do."
US Senator Dianne Feinstein (D-California) said in a statement that Trump called her at 5:30pm and "indicated he would be removing Director Comey, saying the FBI needed a change." Feinstein added that "the next FBI director must be strong and independent and will receive a fair hearing in the Judiciary Committee," of which she is the ranking Democrat.
Acting as FBI director will be Andrew McCabe, who had been the deputy director under Comey. Attorney General Sessions is anticipated to name an interim replacement, while the process to confirm a permanent replacement takes shape.
Comey, 56, was appointed to head the FBI by former President Barack Obama in September 2013. FBI directors typically serve 10-year terms.
The only other time in US history an FBI director has been dismissed was in 1993, when President Bill Clinton and Attorney General Janet Reno pushed out William Sessions amid ethical concerns.
I cringed watching RT's video. Guy in the video acts like Comey was all sloppy and reads a lot into his termination. Clearly hyperbolic. Comey did strike me as pretty careful with his words, as anyone in his position would be. Until he "misspoke," in the FBI's words, which is also something anyone does.