It's an incredible achievement for the Corkman who turns 35 in just under six weeks' time and is showing no sign of hanging up his boots - he signed a two-year contract extension before Christmas that will keep him in red until 2016, at least!
O'Callaghan made his first start for Munster in August 1998 against Edinburgh Reivers in Musgrave Park and it would be quite fitting if he breaks the appearance record almost 16 years later at the same venue.
The achievement is made all the more remarkable by the fact that there were far fewer fixtures at the outset of his career with the Celtic League not forming until 2001.
The Heineken Cup is the competition where O'Callaghan has enjoyed his finest hours as he played a pivotal role as Munster twice became the kings of Europe with Donncha starting both finals.
His Heineken Cup debut came as a replacement against Perpignan in 1998 and he has since played in a further 94 games to lie fourth on the list of all-time most appearances in the competition. O'Gara remains top of that particular list with 110 appearances, another former Munster man, John Hayes is second with Leinster's Gordon D'Arcy in third.
With the landmark record appearance looming, Munster Head Coach Rob Penney gave a glowing endorsement of the one-club man.
"It's a great achievement for Donncha. One great man [O'Gara] being replaced by another great man in the record books, which is what happens. Donncha deserves every plaudit and superlative that you can dish out to him.
"He's been such a great professional for such a long time and he still has a lot left in the tank yet. He's a pretty special athlete and he has a great mentality. I can't speak highly enough about the man and his commitment to Munster," added Penney.
There is no sign of the light dimming on the career of O'Callaghan, in fact if anything it's getting stronger. No Munster player has played in more games for the side this season - O'Callaghan has made 18 appearances out of a possible 19, level with Dave Kilcoyne, and that's not including appearances in both pre-season friendlies.
Apart from his continuing contribution to Munster Rugby, O'Callaghan has also earned 94 Ireland caps in an international career that has, so far, spanned 11 years since his debut away to Wales in the 2003 Six Nations.
Add that to the 12 appearances for the British and Irish Lions, including three tests - two against New Zealand in 2005 and one against South Africa in 2009 - and you have a CV that would stand up against any other in world rugby.
Munster face Zebre at Musgrave Park on Saturday at 6:45pm with tickets available here.