There have been eight changes to the team that lost at the weekend to Munster, with the likes of Ruan Pienaar, Chris Henry and Andrew Trimble all returning to the starting line-up.
Dan Tuohy will also start after recovering from a torn calf muscle, and he joins Lewis Stevenson in the second-row.
Henry will captain Ulster and starts at openside, with Robbie Diack at blindside and Nick Williams at Number 8.
Rob Herring and Adam Macklin are retained in the front row, while Tom Court starts at loose head. Darren Cave and Paddy Jackson will also return to join the back-line.
Ulster confirmed that Rory Best is not included in the squad because he is being rested. Callum Black drops to the bench, as do Neil McComb and Roger Wilson.
Paddy Wallace and John Afoa are also named as replacements, alongside Niall Annett, Michael Heaney and Ricky Andrew.
Ulster won their previous meeting with Scarlets in Wales just last month by 19 points to 12, and they will hope for some redemption after losing their PRO 12 winning record with the defeat to Munster.
Friday night's kick off at Ravenhill is 7:05pm.
A D'Arcy, A Trimble, D Cave, L Marshall, C Gilroy; P Jackson, R Pienaar; T Court, R Herring, A Macklin, L Stevenson, D Tuohy, R Diack, C Henry, N Williams.
Replacements (16-23): N Annett, C Black, J Afoa, N McComb, R Wilson, M Heaney, P Wallace, R Andrew.