"My crime - my biggest crime - is that on another occasion I went in a second time, and that was deliberate.
"That was sitting waiting to vote on the side of the chamber."
He added: "What I did was absolutely wrong. I was wrong, I was stupid, I lost sense of mind."
Parish gave the television interview on Saturday morning after leaving his parents' farm in north Somerset near Bridgwater, where there is an old Claas Dominator 76 combine harvester and a Massey Ferguson 265 tractor in a barn.
Parish denied watching the pornography in a way that he hoped other people in the chamber would see.
"I make a full apology. A total full apology. It was not my intention to intimidate," he said.
He appeared emotional as he explained how overnight he had decided to quit as the Devonshire MP.
"In the end I could see that the furore and the damage I was causing my family and constituency and association and it wasn't worth carrying on," he said.
"What I do want to put on record, for all my rights and wrongs, I was not proud of what I was doing. I was not actually making sure people could see it."
He rejected the suggestion he "was watching it and intimidating women", adding that he had maintained 12 years in Parliament with "one of the best reputations ever - or I did have".
Asked what possessed him to view the pornography in a public place, he replied: "I don't know. I think I must have taken complete leave of my senses, my sensibilities, and a sense of decency - everything.
"I'm not defending what I did for one moment. But, I thought the best thing I could do is tell the truth."
The Tiverton and Honiton Conservatives issued a statement saying it supported his decision to resign, triggering a by-election in the Tory safe seat.
"We would like to take this opportunity to thank Neil Parish for his service to our communities over the past 12 years," a spokesman added.
Parish had been facing an investigation by Parliament's standards commission over the incident. MPs who are found to have violated the code of conduct can face a variety of sanctions, including being ordered to apologise to the Commons or being suspended or expelled.
Labour has criticised the wider culture in Parliament, accusing the Government of having known about the incident for days but had failed to take action.
Caroline Nokes, a senior Tory MP, also criticised the delay by the Tory whips office to act and suspend Parish.
"I felt that by leaving it until Friday before we knew that action had been taken by the whips, that felt like unnecessary dither and delay," she said.