Neil Parish has told the BBC he is resigning as an MP after admitting he watched pornography twice in Parliament.
Mr Parish, who has represented Tiverton and Honiton in Devon since 2010, said it had been a “moment of madness”.
He said the first time was accidental after looking at a tractor website, but the second time – in the House of Commons – was deliberate.
He was suspended by the Conservative Party on Friday over the allegations.
Two female colleagues claimed they had seen him looking at adult content on his phone while sitting near them.
In an exclusive interview with BBC South West, Mr Parish said: “The situation was that funnily enough, it was tractors I was looking at.
“I did get into another website that had a very similar name and I watched it for a bit, which I shouldn’t have done.
“But my crime – biggest crime – is that on another occasion I went in a second time.”
He admitted that second time had been deliberate and that it happened in the House of Commons while he was sitting waiting to vote.
Mr Parish said what he did “was absolutely totally wrong”, adding: “I will have to live with this for the rest of my life. I made a huge terrible mistake and I’m here to tell the world.”
He appeared emotional as he said he was standing down after seeing the furore and damage it was causing his family, his constituency and local association.
“I was wrong, I was stupid, I lost sense of mind,” he said. But he denied watching the material in a way where he hoped other people would see it.
He told the BBC: “I make a full apology. A total full apology. It was not my intention to intimidate.”
Mr Parish’s resignation will trigger a by-election in his Devon constituency, in which the Conservatives held a 24,239 majority over Labour in the 2019 general election.
Shadow Commons leader Thangam Debbonaire said it was “the right decision” for Mr Parish to quit and that the people of Tiverton and Honiton “deserve better”.
“It’s shocking that the Conservatives have allowed this debacle to drag out over many days,” she said.
Angela Rayner, the Labour deputy leader, tweeted: “He was looking for tractors but ended up with porn actors? Neil Parish must think you were all born yesterday.”
The deputy leader of the Liberal Democrats called on the Conservatives to “swiftly call a by-election”.
“It is appalling that Neil Parish had to be pushed to resign after those in charge of the Conservative Party spent days dragging their feet,” said Daisy Cooper.
Scotland’s first minister Nicola Sturgeon said there could have been no other outcome than Mr Parish’s resignation and that his actions had been “unacceptable”.
Mr Parish’s local party, Tiverton and Honiton Conservatives, said it supported his decision to step down and thanked him for his service.
Questioned by the BBC about his wife Sue finding out about the situation through the media, Mr Parish said: “I know I should quite rightly be ashamed of that.”
He said she had been “amazingly supportive” but admitted it was not something he “particularly wanted to discuss with her”.
In an earlier interview with the Times, Mrs Parish said the allegation was “very embarrassing” and described her husband as “quite a normal guy” and “a lovely person”.
“If you were mad with every man who looked at pornography, you would not have many wives in the world,” she said.
Mr Parish – who was also chair of the environmental select committee – had been facing an investigation by Parliament’s standards commissioner.
MPs found to have violated the code of conduct can face punishments including apologising to the Commons, or being suspended or expelled.
Senior Tory MP Caroline Nokes had criticised the delay by the Tory whips office to act and suspend Mr Parish from the Conservative party, saying the whips office was “still too blokey”.
source: BBC