Lions head coach Ian McGeechan has already given the honour of captaining the Lions to O'Gara's Munster team mates Paul O'Connell and Donncha O'Callaghan, as well as Leinster's Brian O'Driscoll.
Cardiff Blues flanker Martyn Williams and Ospreys lock Alun Wyn Jones have also had spells during matches on tour when they have taken charge of the team.
O'Gara will lead a side that contains six players who played against the Springboks in the first Test in Durban. Martyn Williams and Donncha O'Callaghan, who were both second half replacements at the ABSA Stadium, figure in the starting line-up, while Test starters Lee Mears, Phil Vickery, David Wallace and Ugo Monye are among the replacements.
There will be a Lions debut for England prop Tim Payne, while another replacement prop, 2005 Lion John Hayes, joins him in a front row that is completed by Scottish hooker Ross Ford.
Payne was called out to act as cover for Andrew Sheridan, who is suffering from a back strain, and will go straight into the game a day after arriving in Cape Town. Hayes joined the party in Durban on Saturday after flying out to replace the injured Euan Murray.
Ronan O'Gara becomes the third Munsterman to captain the Lions on this tour as he follows in the footsteps of Paul O'Connell and Donncha O'Callaghan.
"There were many positives that came out of the Test match on Saturday. The Emerging Springboks match, and our training this week, will allow us to build on these plus address areas we know we need to improve on," said Lions head Coach Ian McGeechan.
"There is still a lot to play for and the players are well aware of that. The mood in camp is still very positive due to the fact that we did come very close to winning on Saturday and the fact that we created so many scoring opportunities.
"The players are well aware of the importance of the match tomorrow against the Emerging Springboks. We need to step up our performance against a talented outfit whose players, like ours, will be determined to show that they are worthy of a Test place. It should be a great match.
"The two latest squad members, Tim Payne and John Hayes, will start against the Emerging Springboks to give them immediate field time. This is important in terms of the balance of the squad as three of our other props played in the Test match only two days ago and Andrew Sheridan is recovering from injury.
"Ronan O'Gara will lead the team against the Emerging Springboks which is a well deserved honour for a senior player who has served Munster, Ireland and the British & Irish Lions with distinction."
British & Irish Lions ( v Emerging Springboks)
15. Keith Earls (Munster/Ireland)
14. Shane Williams (Ospreys/Wales)
13. Riki Flutey (London Wasps/England)
12. Gordon D'Arcy (Leinster/Ireland)
11. Luke Fitzgerald (Leinster/Ireland)
10. Ronan O'Gara (Munster/Ireland, Captain)
9. Harry Ellis (Leicester Tigers/England)
8. Andy Powell (Cardiff Blues/Wales)
7. Martyn Williams (Cardiff Blues/Wales)
6. Joe Worsley (London Wasps/England)
5. Nathan Hines (Perpignan/Scotland)
4. Donncha O'Callaghan (Munster/Ireland)
3. John Hayes (Munster/Ireland)
2. Ross Ford (Edinburgh/Scotland)
1. Tim Payne (London Wasps/England)
Replacements
16. Lee Mears (Bath/England)
17. Phil Vickery (London Wasps/England)
18. Simon Shaw (London Wasps/England)
19. David Wallace (Munster/Ireland)
20. Mike Blair (Edinburgh/Scotland)
21. James Hook (Ospreys/Wales)
22. Ugo Monye (Harlequins/England)
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