Former Ireland skipper Best is calling time on a 15-year senior career after Saturday's match at Twickenham.
It has now been confirmed the 37-year-old will lead Eddie Jones' side, with the England coach having also included three of South Africa's Rugby World Cup winners.
Makazole Mapimpi and loosehead prop Tendai Mtawarira – also making the final appearance of his career – start, with Lukhanyo Am named on the bench.
In total, there are 10 South African players within the 23-man invitational squad.
Best's final international appearance for Ireland came in their 46-14 defeat to New Zealand in the World Cup quarter-finals.
Barbarians: 15. David Havili, 14. Dillyn Leyds, 13. Mathieu Bastareaud, 12. Andre Esterhuizen, 11. Makazole Mapimpi, 10. Curwin Bosch, 9. Joe Powell; 1. Tendai Mtawarira, 2. Rory Best, 3. Enrique Pieretto, 4. Luke Jones, 5. Tyler Ardron, 6. Pete Samu, 7. Marco van Staden, 8. Josh Strauss.
Replacements: 16. Andrew Makalio, 17. Campese Ma'afu, 18. Hencus van Wyk, 19. Angus Cottrell, 20. Matt Philip, 21. Jano Vermaak, 22. Lukhanyo Am, 23. Morne Steyn.