Leinster welcome back two stars to their starting XV for the Guinness Pro14 clash against Glasgow on Saturday.
Robbie Henshaw and Devin Toner start at centre and second-row respectively, neither player having played since the Six Nations.
O'Brien starts at openside flanker and will captain the side.
Rob Kearney starts at full-back alongside Jordan Larmour and Dave Kearney on the wings, while Joe Tomane partners Henshaw in the centre.
Jamison Gibson-Park and Ross Byrne are the half-backs.
Ed Byrne, James Tracy and Michael Bent pack down in the front-row with Toner (below) and academy lock Jack Dunne behind them in the engine room.
Caelan Doris starts at No 8 with Josh Murphy joining O'Brien as flankers.
Will Connors has been named on the bench and could make his first appearance since suffering a knee injury in August. If he plays, he will become the 56th player used by head coach Leo Cullen this season.
Kick-off at the RDS is at 3pm on Saturday.
Rob Kearney, Jordan Larmour, Joe Tomane, Robbie Henshaw, Dave Kearney, Ross Byrne, Jamison Gibson-Park; Ed Byrne, James Tracy, Michael Bent, Devin Toner, Jack Dunne, Josh Murphy, Seán O’Brien, Caelan Doris
Replacements: Seán Cronin, Cian Healy, Tadhg Furlong, Will Connors, Max Deegan, Hugh O’Sullivan, Ciarán Frawley, Adam Byrne