The move comes after it was reported Wednesday night that Sessions had two meetings with the Russian ambassador to the U.S. in 2016 after he started supporting Donald Trump's presidential bid and then failed to disclose the contacts during his confirmation hearing.
"Let me be clear: I never had meetings with Russian operatives or Russian intermediaries about the Trump campaign," Sessions told reporters. "And the idea that I was part of a continuing exchange of information during the campaign between Trump surrogates and intermediaries to the Russian government are false."
During an interview with Fox News' Tucker Carlson Thursday night, Sessions emphasized, "Recusal is not an admission of any wrongdoing. It's simply ... whether or not you can be perceived as fairly deciding a case."
In a statement, Sessions said that over the last several weeks he met with "relevant senior career department officials" to discuss whether he should recuse himself and, "having concluded those meetings today, I have decided to recuse myself from any existing or future investigations of any matters related in any way to the campaigns for president of the United States."
Sessions held a press conference Thursday afternoon to announce the decision, saying that his reply to Sen. Al Franken, D-Minnesota, during his confirmation hearing for attorney general "was honest and correct as I understood it at the time."
"In the end, I have followed the right procedure, just as I promised the committee I would," Sessions said of the decision to recuse himself.
"A proper decision, I believe, has been reached," he said.
Earlier Thursday in Virginia, Trump said that he had "total" confidence in Sessions, that Sessions "probably did" answer questions truthfully at his confirmation hearing and that he didn't think Sessions should recuse himself. A White House official dismissed the matter as "the latest attack against the Trump administration by partisan Democrats."
A Department of Justice official said Wednesday night that Sessions had two contacts with Russian Ambassador Sergey Kislyak — one with members of his staff on Sept. 8 (which was listed on his public schedule) and one after giving a speech to the Heritage Foundation in July.
Michael Flynn, Trump's former national security adviser, resigned after misleading the vice president and other White House officials about contacts with Kislyak.
Asked about the nature of the September meeting on Thursday, Sessions told reporters, "I don't recall any particular political discussions."
He said that he didn't remember a lot of the meeting but that "I do remember saying I had gone to Russia with a church group in 1991."
"So we talked a little bit about terrorism, as I recall. Somehow the subject of the Ukraine came up. I had the Ukrainian ambassador in my office the day before to listen to him," he said. Apparently paraphrasing Kislyak, Sessions added, "Russia had done nothing that was wrong in any area and everybody else was wrong with regard to the Ukraine. It got to be a little bit of a testy conversation at that point."
The DOJ official said Wednesday that during the 2016 campaign, ambassadors made "superficial comments" about the election but it wasn't the "substance of their discussion."
Sessions told reporters he didn't recall having met Kislyak any other times. "It's possible. I'm on the Armed Services Committee," he said. "Things happen. I don't recall having met him before that."
Asked if he met with any other Russian officials since endorsing Trump, Sessions said, "I don't believe so."
He was the first sitting senator to endorse Trump, in February 2016, and became the chairman of his national security advisory committee the next month.
A DOJ spokeswoman said in a statement Wednesday night that the meetings stemmed from Sessions' role at the time as a senator on the Armed Services Committee and that his answers during the confirmation process were not "misleading."
During his confirmation hearing for attorney general in January, Sessions said he "did not have any communications with the Russians."
On Thursday, Sessions conceded, "Retrospect, if — I should have slowed down and said, 'But I did meet one Russian official a couple times." That would be the ambassador."
With Sessions' recusal, responsibility for overseeing any DOJ matters within the scope of the recusal fall to the deputy attorney general.
The nominee for that position, Rod Rosenstein, currently the U.S. attorney for Maryland, has not been confirmed yet, however. His confirmation hearing is scheduled for Tuesday, March 7.
Until that appointment is made, the acting deputy attorney general, Dana Boente, the U.S. attorney for the Eastern District of Virginia, will likely be the person responsible for such matters at the DOJ.
In those matters, the deputy attorney general or acting deputy will have the authority to appoint a special counsel.