The Ukip leader said on Sunday he would be willing to stand in a court of law and say that he was at the ground on the day of the tragedy.
Meanwhile, he said he had suffered "moments of doubt" over whether he is the right person to lead Ukip as the party deals with the fallout from defeat in the Stoke by-election.
Mr Nuttall had to apologise in the run-up to the by-election over a false claim that he lost close friends in the disaster.
But he told the BBC's Andrew Marr Show that suggestions he was not at the stadium were untrue.
He said: "There was an orchestrated smear campaign which I knew was coming from December which was suggesting that I wasn't actually at Hillsborough.
"Can I just put this on record Andrew, because this is really important?"
When pushed on who was behind the alleged smear campaign, he said: "There was an orchestrated campaign which I knew was coming which was done by a political party. I'll leave it at that, okay?"
When asked if he was referring to the Labour Party, he said: "Yes. I am actually. Yes, I am, okay? They suggested that I wasn't actually at Hillsborough.
"I provided witness statements, I have given evidence to Operation Resolve and I'm prepared to stand in a witness stand in a court of law."
Mr Nuttall said people needed to get "perspective" on the issue.
He said: "It's not as if I have lied about weapons of mass destruction. It's not as if I have taken us into an illegal war.
"It's not as if I've been caught in a paedophile gang or anything."
Mr Nuttall declined to name the person who he previously said he knew who had lost their life at Hillsborough.
Meanwhile, the Ukip leader admitted the Stoke defeat had made him suffer some doubts over his leadership.
He said: "I have never thought I was the wrong guy. I mean of course you do have moments of doubt."