The firing comes as the FBI is conducting a counterintelligence investigation into Russian meddling in the 2016 election, including any possible links between Trump campaign associates and Moscow.
Here is a timeline of the consequential moments of Comey's tenure during the heat of the 2016 election and after:
July 5, 2016: Comey recommended that the Justice Department does not charge Hillary Clinton, the eventual Democratic nominee for president, for her handling of classified information at the State Department. While Comey said Clinton and her associates were "extremely careless" with classified information, he said no "reasonable prosecutor" would bring charges in the case. Top Justice Department officials cited Comey's handling of the case when they recommended that Trump fire him.
Oct. 28, 2016: In a letter to Congress, Comey said the FBI uncovered new emails that could be related to the Clinton investigation. They were discovered during an investigation into disgraced politician Anthony Weiner, who is married to Clinton aide Huma Abedin. The letter came just days before the presidential election and featured prominently in news coverage in the race's final days.
Nov. 6, 2016: Two days before the election, Comey told Congress that the newly discovered emails did not change the FBI's conclusion that no charges were warranted in the Clinton case.
March 20, 2017: Comey publicly confirmed the FBI's counterintelligence investigation into Moscow's role in the 2016 election, including any possible links between people associated with the Trump campaign and Russia. The U.S. intelligence community previously concluded that Russian President Vladimir Putin directed efforts to influence the election. Trump has repeatedly denied any collusion with Russia and has even suggested at times that Moscow may not be responsible for a high-profile cyberattack against the Democratic National Committee.
May 3, 2017: At a Senate oversight hearing, Comey said he stood by his decision to send the October letter to Congress, adding that he would "make the same decision" again. "It makes me mildly nauseous to think we might have had some impact on the election," Comey said.
Tuesday: Trump fires Comey, telling him in a letter, "it is essential that we find new leadership for the FBI that restores public trust and confidence in its vital law enforcement mission."