The Galway native became the first Irish rugby coach to collect the accolade since the late Mick Doyle was honoured in 1985 for his part in guiding Ireland to it's last Triple Crown 19 years ago.
It was a memorable year for Irish rugby under the guidance of O'Sullivan, with the defeat of England in Twickenham a highlight which started the ball rolling towards victories over Wales,ltaly and Scotland to give Ireland the Triple Crown and second place in the RBS Six Nations Championship.
It also caps off a memorable year for Irish rugby after O'Sullivan guided the team to three win out of three in the autumn international series, including victory over Tri Nations Champions South Africa.
"Mick was a huge loss. He always had an impact on the game, whether as a player, a coach or a pundit and we all enjoyed Mick at every level of the game," O'Sullivan said.
In winning the award, O'Sullivan beat off strong challenges from Shelbourne Manager Pat Fenlon, All Ireland winning Kerry football manager Jack O'Connor and Cork hurling manager Donal O'Grady.
The awards were dominated by rugby. Former Ulster coach Alan Solomons took December (2003), Alan Gaffney was the January winner and Shannon coach Geoff Moylan took the award in May for his part in winning the AIB League final in May.
Eddie O'Sullivan and the rest of Irish rugby, including the provincial coaches will be hoping that 2005 will be an even better year.