Prior to yesterday, Mr Mahon, aged 52, had a profile which was considerably less than that of his retired predecessor. That is now changed.
Despite making the news for matters other than his helmsmanship of the tribunal, Mr Mahon may yet see the job through over the next 15 years.
There may have been a miscalculation in his tax affairs back in the ’80s, but on matters legal rather than fiscal there’s little danger of this man making a slip.
The law is Mahon’s life in every sense of the word - his father was a lawyer and a judge; his three brothers are lawyers; he married a lawyer and his wife comes from a family of lawyers.
Originally from Tullamore, Co Offaly, his early career was spent in provincial courts in the Midlands. He has been described as a family man and a practising Catholic.
Judge Mahon's grandfather, James, was a self-made man, a public servant who went on to set up a chain of cinemas in the Midlands. And young Alan is reported as having spent much of his youth in the local Ritz and Grand Central cinemas in Tullamore.
His father Seamus was a District Court judge from 1974 to 1989. There was controversy over his retirement at the age of 70, which ultimately led to the passing of legislation designed to get over legal problems regarding his decisions after the age of 65.
The second of four sons, he was educated in the exclusive Clongowes Wood in Co Kildare. His three brothers trained as solicitors and went into the family firm of Hoey & Denning in Tullamore. Judge Mahon trained as a barrister in King's Inns.
He was called to the Bar in 1976 and became a senior counsel in 1988.
His wife Anne Marie Reidy came from a Co Kildare legal family, and the family home is in Naas. He is father of four children, ranging in age from 14 to 21 years.
Tribunal chairpersons are usually drawn from the ranks of the High Court, but the new chairman was a Circuit Court judge who had been on the Bench for just over a year.
In June 2001, Mr Justice Flood asked the Government for extra members to help him with the workload of the tribunal. Eight months later, the Government announced the appointment of Mahon, then still a senior counsel, Mary Faherty SC, as well as a reserve member, barrister Gerald Keys.
The new members first had to become judges and this required legislation to increase the permissible number of circuit court judges. It wasn't until October, 2002, that they were appointed to the tribunal.
"He wouldn't move in fashionable circles. He's certainly not part of the Shelbourne bar set," one acquaintance has been reported as saying.
"He can talk as good as any lawyer, but he's a good listener, too. And it doesn't matter to him what your station in life is, he's still happy to share a conversation with you," another was reported as saying.
At some stage as chairman, he's going to have to read over one million lines of transcript, the result of four years of tribunal hearings. That's just to put him in a position to decide on the issue of legal costs, which itself is bound to entail further hearings and litigation.
Few people who have had contact with Judge Mahon have anything mildly critical to say about him. Some remember his application to complex legal work, others his ability to deliver within strict deadlines. He is said to have a gift for storytelling, and is generally regarded as a serious person.
When Judge Flood retired, Mr Mahon was willing to take on a job with the tribunal, when more senior colleagues declined. Since then he has not been shy in criticising the obfuscation of chief witness, Liam Lawlor.
After three stints in Mountjoy for obstructing Mr Justice Feargus Flood, Judge Mahon decided the powers available to the DPP might be more influential on the behaviour of Mr Lawlor.
If successfully prosecuted for repeatedly lying to Mr Mahon and his predecessor, Mr Lawlor could face up to two years behind bars or a fine of €300,000.