He arrived in Dublin on a summer's evening, fresh from the hell of the H-Blocks. On the blanket protest, he'd been beaten black and blue by prison officers. He endured 53 days on hunger-strike, then watched his comrades die. His marriage broke up when he was in jail.

On his first night in Dublin, he slept in a car. His economic prospects didn't look good. An ex-IRA prisoner with £240 to his name, hoping to find work on a building site.

Twenty years later, Tom McFeely, multi-millionaire property developer, opens the door to his Ailesbury Road mansion, which was once the former German embassy. "It's a bit different to my Long Kesh cell," he grins.

It's a magnificent house, teeming with white marble fireplaces, ornate ceilings and chandeliers. A Celtic cross engraved with the hunger-strikers' faces adorns a rosewood dresser. Long Kesh harps sit beside priceless tapestries. He opens a drawer to search for pictures of himself and his comrades in the H-Blocks.

Buried under the photos is an original Picasso etching. "I haven't bothered hanging it," he says. Tom McFeely is a man who does things his way. In business, he is as controversial as he is successful. This is the first interview he's ever given. His rags-to-riches "transformation"– from militant republican to millionaire – has been widely covered in the media.

"Transformation!" he declares. "There has been no transformation. I've just brought the energy and determination I gave to the IRA to the world of business. I will always be a republican. My republican convictions are as strong as ever – they couldn't be stronger.

"Most other big property developers turn their noses so far up at me, they could be used as flag-poles. I've no time for them either. They are arrogant, egotistical and anaemic. I've far more respect for street sweepers, the bar-men in my local, indeed anybody, than I have for most property developers."

McFeely (60) is at the centre of a legal battle which opens in Dublin High Court on Tuesday and is expected to last two months. It focuses on the Tallaght Square shopping-centre development, and will expose the rivalry between Ireland's richest property developers.

McFeely, his business partner Larry O'Mahony, and billionaire Liam Carroll, are being sued by Noel Smyth, the solicitor turned property developer. Smyth is seeking €130m damages from the trio for alleged breach of contract, and loss of tax breaks and profits, relating to delays in the development. McFeely is challenging the claim. "I expect to win," he declares.

He picks me up from Connolly Station in a 1994 yellow-and-black-striped sports car – "the Bumble Bee", he calls it affectionately. The best a passenger can do is hold on tight and hope for the best. He races around successive corners, squeezes between buses, and then makes a mad manoeuvre to the right into Ailesbury Road.

I'd read he drove a Bentley. "There it is," he says pointing to the Bentley parked in the driveway. "It cost me €279,000 and I've put only 12,000 miles on it in four years. I just bought it to sicken Cab [Criminal Assets Bureau]. I'd to give them €9m in unpaid taxes. When I wrote the last cheque, I went out and bought the Bentley. I was saying, 'F**k you!'"

Most Cab officials and gardaí are "decent people only doing their jobs, but a minority are nasty individuals with an agenda", he claims. When he was dating his American girlfriend, gardaí visited her regularly: "They'd check her visa and ask her if she knew who she was going out with." The couple are now married with two teenage children. McFeely has three grown-up daughters in the North from his first marriage.

He refuses to disclose his financial worth – "sure some people say I'm worth nothing!" But the Ailesbury Road property is valued at €15m. He has a €6m holiday home on the Algarve, where he also owns a hotel. He co-owns the Tallaght Plaza Hotel and he's involved in building projects in the Republic, London, and Manchester.

He was born in Dungiven, Co Derry, into a family of 13. His father was a cattle-dealer – "that's where I learned my entrepreneurial skills". His republicanism came from his mother.

He was in London working as a brick-layer when the civil rights marchers were beaten off Derry's streets in October 1968. He came home and joined the IRA. He was on the January 1969 march when loyalists stoned civil rights protestors in Maghera: "I ran into a builder's yard, grabbed a hatchet, and went at the loyalists." He was charged with riotous behaviour.

In 1971, a British soldier stopped him as he drove a car bomb. He thumped the soldier, escaped, and went on the run. McFeely refers to the shooting of a UDR major the following year: "Our family home had been raided during the IRA border campaign.

"I was only a child but I never forgot the hatred contorting the face of one B-Special as he wrecked our house. That man later joined the UDR. He was shot outside his own home in 1972." I ask McFeely if the soldier died. "He was hit by a 303 [rifle] from five feet. What do you think?" he replies unflinchingly. No one was ever charged with the murder.

In 1974, McFeely was arrested with guns in Leitrim and imprisoned in Portlaoise. Within three months he escaped, using a bomb to demolish a prison wall. In 1976, he was recaptured, with another IRA man, after a gun battle with the RUC. He was charged with attempted murder of police, possession of weapons, and a post office robbery.

His co-accused was sentenced to 12 years' imprisonment; McFeely to 26 years. "You are an extremely dangerous, intelligent and vicious young man," the judge said. "I may serve this term, but you won't," McFeely shouted from the dock.

He was a small man, but he was muscular. "In Long Kesh, if the screws were beating up young prisoners, or throwing piss pots around them, they'd have Tom to answer to. He'd break their jaws," recalls another prisoner. "It always took a whole team of screws to visit Tom's cell. He gave, and took, many beatings. He was so hard, we'd say 'he wasn't born, he was chiselled'."

Such was his influence that in 1978 the prison authorities housed McFeely in isolation. He went on an 11-day hunger-and-thirst strike. "The tips of my fingers and toes went black. My tongue was swollen like a balloon. I could smell water. I wasn't sweating, so the heat in my body was unbelievable." He was approaching death when the authorities capitulated and returned him to the IRA wing.

Two years later, he joined the first hunger-strike, enduring 53 days without food before it was called off: "I never once felt hungry but I was blind by the end and I felt constantly nauseous. I was vomiting green bile. I think I'd have lasted another few weeks but I was fully prepared to die."

Remarkably, he volunteered for the second IRA hunger-strike, led the following year by Bobby Sands. But the IRA leadership believed his body was so weakened from his previous fasts that he would die too quickly.

At one stage, McFeely was himself OC of the blanketmen but most times he clashed with the IRA leadership. He criticised the 1983 H-block escape in which 38 inmates left in a prison van. "Only those willing to return to IRA active service should have been allowed to escape. Far too many who had no intention of doing that got out."

By the mid-1980s, he was totally disillusioned with the leadership. "I argued with other prisoners who were pleased at Sinn Féin taking votes off the SDLP. I told them Sinn Féin, not the SDLP, would destroy the IRA, and I was right. The leadership were intent on a deal far short of a British withdrawal and a united Ireland. It was immoral to continue armed struggle in such circumstances."

On release from jail in 1989, he headed to Dublin. In those early years on the building sites, he worked hard, saved what he could, borrowed more money, and invested it. He made his fortune through land deals and property developments.

He doesn't speak to his Ailesbury Road neighbours: "I keep myself to myself." His "weakness" is eating out and a few bottles of wine. Other indulgences are his Jacuzzi and sauna. He doesn't really "enjoy holidays". Every few minutes, his mobile rings or beeps with texts. He never turns it off. He sleeps no more than five hours a night. "The wife says she gets a good night's rest only when she goes on holiday."

He doesn't like socialising with other big businessmen. "I went to a polo-club event once. The boxer, Steve Collins, came in and everybody looked down on him. There were rumours he had beaten his wife."

(Collins has always denied these rumours.)

"I've no time for domestic violence but these men's attitude to Collins was class-based. There were 22 of us at the table so I said: 'Research shows one man in five hits his wife, so four of us here have done it. Put your hands up boys!'" The table fell silent.

McFeely hates Fianna Fáil. His comments about Bertie Ahern are unprintable and "don't even mention that f***er Albert Reynolds ever lived on the same street as me, I despise him", he says.

So what does he make of Mary Lou? "There was a 'come-for-wine-and-canapés-and-meet-Mary-Lou-thing' for business people at a Smithfield hotel. I went along. It was unrecognisable from anything I fought for. I looked around the room. It was many things, but it wasn't republican."

On his building sites, a suited McFeely is often seen laying the first course of brick or showing a man how to sledgehammer down a wall. Despite the recession, he refuses to lay off workers: "We'll all go down or nobody will go down. I'm paying men when there's no work for them, but you don't get loyalty if you don't give it."

He doesn't "do charity – there's no halo around my head". But he recently lent one ex-IRA prisoner €35,000 for a mortgage down-payment. He's done the same for many others and for immigrants struggling to get on their feet. He has sponsored pro-Palestinian walks: "I support the Palestinians, Afghans and Iraqis who are struggling for freedom as we did ourselves."

McFeely was a left-wing radical in Long Kesh. The collected works of Lenin, which he read in jail, sit on his Ailesbury Road bookshelves.

"Look, despite my success under capitalism, I'd have no problem trying socialism in Ireland. But, in the meantime, I have to live. And I might as well live as good as the next!"