O'Connell has recovered from knee and back injuries and is set to play for the first time since Munster's RaboDirect PRO12 win over Ulster back in May.
O'Callaghan sat out Wednesday's training session at Cork IT and was quite hopeful of being fit, but this afternoon the call was made to withdraw him from the squad.
Elsewhere in the pack, David Kilcoyne retains the number 1 jersey in the absence of Wian du Preez who sustained a knee injury against Leinster. It will be the 23-year-old Limerick man's Heineken Cup debut.
Meanwhile, Donnacha Ryan's experience was a probable factor in him getting the blindside berth ahead of David O'Callaghan who is named on the bench.
Speaking of O'Connell's inclusion, Munster head coach Rob Penney said: "We've always maintained that he'd be back when he felt he was ready. I think it's great for us.
"It's great for Irish rugby, for the rugby community to see a player of his calibre back playing again. It was a gradual process. In the interests of the player it had to be."
In the back-line, Ian Keatley comes in at full-back for Denis Hurley, who will hope to have an impact off the bench, while the injured Keith Earls makes way for James Downey in the centre.
MUNSTER (v Racing Metro 92): Ian Keatley; Doug Howlett (capt), Casey Laulala, James Downey, Simon Zebo; Ronan O'Gara, Conor Murray; David Kilcoyne, Damien Varley, BJ Botha, Billy Holland, Paul O'Connell, Donnacha Ryan, Sean Dougall, Peter O'Mahony.
Replacements: Mike Sherry, Marcus Horan, Stephen Archer, David O'Callaghan, Paddy Butler, Peter Stringer, Danny Barnes, Denis Hurley.