O'Brien will make his first competitive start for the province having come on as a replacement last weekend. The Athenry native came up through the ranks at Monivea RFC before moving to Clontarf two seasons' ago. He joined Connacht in the summer.
Justin Meagher will take O'Brien's place on the bench for the Saturday evening clash in Musgrave Park Cork (KO 8:05pm). Darren Yapp misses the game through injury, as does Mark McHugh. Bernard Jackman remains unavailable due to international commitments.
Connacht: 15. David Slemen; 14. Ted Robinson, 13. Matt Mostyn, 12. Niall O'Brien, 11. Conor McPhillips; 10. Paul Warwick, 9. Tom Tierney; 1. Adrian Clarke, 2. John Fogarty, 3. Peter Bracken, 4. Christian Short, 5. Andrew Farley, 6. John Muldoon, 7. Matt Lacey, 8. John O'Sullivan.
Replacements: 16.Henry Bourke, 17. Stephen Knoop, 18. Michael Carroll, 19. Paul Neville, 20. Conor O'Loughlin 21. Eric Elwood, 22. Justin Meagher.