While O'Callaghan was capped in New Zealand in 2005, there will be Lions debuts for Cardiff Blues wing Leigh Halfpenny and Leinster utility back Luke Fitzgerald.
Although Fitzgerald played on the wing for Ireland throughout their Grand Slam campaign, and for Leinster as they won the Heineken Cup for the first time, he is chosen at inside centre for the Bloemfontein clash.
With Riki Flutey still carrying a knee strain from the opening fixture against the Royal XV, and Jamie Roberts needing a break after two successive starts, Fitzgerald has been given the No 12 shirt to complete an all-Ireland centre pairing.
Munster's Keith Earls will get his second start on tour after recovering from the sore shoulder he suffered in the opening victory in Rustenburg.
Halfpenny finally gets his chance to wear the Lions jersey after linking up with the squad this week following eight days of intensive physiotherapy and treatment at his club. He will form an all-Welsh back three with Lee Byrne and Shane Williams.
England scrum-half Harry Ellis gets his first start after an eight-minute cameo against the Golden Lions on Wednesday night. He will partner James Hook at half-back.
Up front, Scotland's Ross Ford and Euan Murray will get their first starts in a front row that is completed by Andrew Sheridan, who has recovered from his appalling blisters.
Wales No8 Andy Powell and Irish flanker Stephen Ferris, who both had to pull out of the opening fixture and then came on as replacements on Wednesday, get their first starts in the back row. England's Joe Worsley joins them, but switches from blindside to openside from his first outing in Rustenburg.
Gordon D'Arcy, the Ireland and Leinster centre who joined the tour this week to provide extra midfield cover, is included among the replacements. He made his Lions debut against Argentina in 2005 and played six times in New Zealand.
Five players who started in the opening game - Matthew Rees (hooker), Adam Jones (prop), Simon Shaw (lock), Ronan O'Gara (outside-half) and Mike Bliar (scrum-half) - appear among the replacements. Nathan Hines, who started at lock on Wednesday night, joins them as cover for the back row.
British & Irish Lions (vs Vodacom Free State Cheetahs)
15. Lee Byrne (Ospreys / Wales)
14. Leigh Halfpenny (Cardiff Blues / Wales)
13. Keith Earls (Munster / Ireland)
12. Luke Fitzgerald (Leinster / Ireland)
11. Shane Williams (Ospreys / Wales)
10. James Hook (Ospreys / Wales)
9. Harry Ellis (Leicester Tigers / England)
8. Andy Powell (Cardiff Blues / Wales)
7. Joe Worsley (London Wasps / England)
6. Stephen Ferris (Ulster / Ireland)
5. Paul O'Connell (Munster / Ireland - Captain)
4. Donncha O'Callaghan (Munster / Ireland)
3. Euan Murray (Northampton Saints / Scotland)
2. Ross Ford (Edinburgh / Scotland)
1. Andrew Sheridan (Sale Sharks / England)
16. Matthew Rees (Scarlets / Wales)
17. Adam Jones (Ospreys / Wales)
18. Simon Shaw (London Wasps / England)
19. Nathan Hines (Perpignan / Scotland)
20. Gordon D'Arcy (Leinster / Ireland)
21. Ronan O'Gara (Munster / Ireland)
22. Mike Blair (Edinburgh / Scotland)