But the the FBI director said any suggestion he had affected the outcome of the November presidential election by making public further investigation of the former secretary of state made him "mildly nauseous."
Comey said he went public on Oct. 28 -- before the Nov. 8 election between Clinton and Donald Trump -- because he believed his agents possibly found emails that could deal with Clinton's reasons for using a private email server. Comey said that failing to inform Congress at that time would be an "act of concealment."
After Comey's opening statement before the House Intelligence Committee, Comey revealed details about how Clinton's emails ended up on the computer of Weiner, a New York Democrat who was married to a top aide to Clinton, Huma Abedin. Weiner was being investigated for possible inappropriate communications with a minor.
"Somehow, her emails were being forwarded to Anthony Weiner, including classified information,'' Comey said.
He explained what led to a reopening investigation after determining in July that Clinton committed no criminal wrongdoing.
"On Oct. 27, the team that had finished its investigation into Clinton's email server asked to meet with me," Comey explained. "What they could see from the metadata that they found on Anthony Weiner's laptop is that there were thousands of new emails, including what might be the missing emails from her Verizon Blackberry."
"So I authorized them to seek a search warrant, and then I faced a choice. I sat there that morning and I could not see a door labeled 'no action here.' There were two doors: One was labeled 'speak,' the other was labeled 'conceal.' Having repeatedly told this Congress that there's nothing there -- to restart and potentially find emails and not speak about it would require concealment. So, to speak would be really bad. But concealment in my view, would have been catastrophic."
"Choosing between 'really bad' and 'catastrophic,' I told my team we had to tell Congress. They worked night after night and found thousands of new emails that included classified information ... but we ultimately found nothing that changed our view about [Clinton's] intent. It makes me mildly nauseous to think that we might have had some kind of impact on the election. But tell me, what you would do in that position? Would you speak, or would you conceal? In hindsight, I would make the same decision. I would not conceal that from Congress."
Sen. Dianne Feinstein of California, the ranking Democrat on the committee, demanded to know why he treated the investigation of the emails and whether any Trump associates might be working with Russian officials to meddle with the presidential campaign so "dramatically different."
"We treated the Russia investigation like we did the Clinton investigation," Comey said, adding that the FBI didn't reveal the existence of either investigation until months after they began.
The FBI had already concluded that Russian intelligence hacked into Democratic computer systems and email accounts. The information was published by WikiLeaks during the campaign.
The committee also wants to examine leaks to the news media and the use of wiretapping as an investigative tool.
"We need the FBI to be accountable because we need the FBI to effective," said committee chairman Sen. Charles Grassley, R-Iowa.
Grassley's first question was about leaks, asking him if he'd ever been an anonymous source for stories about Clinton or Trump.
"Never,'' Comey said. Asked if he'd authorized anyone to speak anonymously to reporters about those cases, the director said "no."
On Tuesday, Clinton said Comey's decision on Oct. 28 to tell Congress his investigators were looking at a new batch of Clinton emails helped alter the outcome of the presidential election.
"If the election had been on Oct. 27, I would be your president,'' she said at an event in New York.
Late Tuesday, Trump responded on Twitter: "FBI Director Comey was the best thing that ever happened to Hillary Clinton in that he gave her a free pass for many bad deeds! The phony Trump/Russia story was an excuse used by the Democrats as justification for losing the election. Perhaps Trump just ran a great campaign?"
In his prepared statement, Comey said, "I love this work, I love this job, and I love it because of the mission and the people I get to work with,'' he said.