Before being locked up he was an Ulster Volunteer Force bomber. Arrested while transporting an explosive device, he spent five years in jail, using the time to rethink his philosophy before his release in 1980. He emerged not as a pacifist; he was still a unionist, but now a socialist as well.
Today, he is grass-roots loyalism's most articulate political spokesman and one of the leaders of the Progressive Unionist Party who helped stitch together the accord that may decide Northern Ireland's future when it goes to referendum on 22 May.
He believes in the agreement: "It's not the case that there is no alternative and we have to take this no matter how bad it is. I think unionism gets a good deal out of this, if we can get past the emotional pain," he says.
"It offers an opportunity to live together; or maybe, to be cynical about it, it offers the opportunity to see whether we can live together or not. It is certainly what we require to allow this divided society to function."
While nationalists are likely to give overwhelming support to the accord, the unionist and loyalist communities are undecided. Sitting in an office on the Shankill Road, the heartland of Belfast loyalism, Mr Ervine describes Protestant mood swings.
"One day I find people saying they can't vote Yes because it would let Gerry Adams into the executive, would let all these prisoners out, or because there's no arms handed in, because people haven't paid enough attention to the victims, or because they think somebody's going to stuff the Irish language down their throat. Then, next day, I'm being congratulated on the agreement. I'm convinced there is a massive swath of people out there who are not committed yet in one direction or the other."
He reflects on the man leading the No campaign, the Rev Ian Paisley. "We all, as kids, listened avidly to Paisley telling us we were sold out. I listened to the rhetoric. I can't say he made me do anything; I made my own conscious decisions in terms of involving myself in paramilitarism. But I don't think any of us can be divorced from the atmosphere that was created, the atmosphere that people like himself helped to create.
"Now he's putting up no alternative to the agreement. It's all too easy to suggest that Paisley is in demise, but if people are frightened enough, and religious enough, then indeed he might do all right."
Ervine uses the word "pain" on a number of occasions, most often to signify the feelings of those who, under the agreement, will watch the early release of both republican and loyalist prisoners, some of whom have been convicted of murder. He first makes the point that while scores of prisoners will qualify for early release, the fact is that 10,000 or more have, over the years, been released in the normal course of events.
"Prisoners are driving the buses, they're serving behind counters, they're sweeping the streets," he says. "Indeed some of them are lecturers in universities. If we're about pulling down the curtain on the past, are the 300-odd prisoners still in Long Kesh to be held there forever on the basis that they're responsible for the past 800 years of history? I realise the pain of it. But they will be released on licence, and it could become an anchor to keep people wedded to the democratic path."
Asked who impressed him during negotiations, he gives an unexpected answer, singling out two nationalists, Seamus Mallon and Mark Durkan of the SDLP. Next he mentions unionist leader David Trimble: "Somewhat to my surprise, he rose massively in my estimation, showing skill, courage and fortitude."
And the republicans? "I do not trust the Provos. We're all bound to wonder whether they will operate a dual strategy, with Sinn Fein playing revolutionary, in-your-face politics in the chamber as the IRA rumble on outside.
"These are things for unionism to worry about. But there's only one way to find out: go for the agreement and flush out those who can't abide by democratic parameters. This agreement will show whether we can live together."Reuse content