Head coach Nigel Davies has chosen to bring back the influential and experienced outside half a week before the Scarlets' opening European cup game against Brive at Parc y Scarlets on October 10th.
Jones was rested as a precaution at last weekend's high profile Welsh derby last weekend in Cardiff, to recover from a slight ankle injury.
Davies said: "Stephen will play for us on Friday which will give him an opportunity to roll into the European game. He's massive for us - he has that level of experience and mental toughness on the field that we need for this game. He brings a real composure and understanding to the team and does boss games particularly well."
"It's not only what he does on the field, it is what he contributes off the field as well and he is hugely respected by all the guys."
On preparations for Ulster, the Scarlets head coach said: "It's a short turnaround for us, however we are comfortable, we know where we are and what we want to do. We are going to have to be that much better than them to win up there and be on top form to get a result; but in any case that's where we need to be now going into Europe."
The Scarlets will rest captain Mark Jones, who picked up a dead leg against the Blues, as well as player-coach Simon Easterby, who left the field after aggravating a knee problem.
Flanker Johnathan Edwards makes his first start of the season ahead of Richie Pugh at openside, a reward for Edwards's impressive form at semi-pro level for Llandovery.
Wales prop Rhys Thomas will also return to the side having missed the last two matches with stitches in a cut knee.
Captain Mark Jones said Friday's encounter will be about registering much needed points in the league and said his Wales team mate's return would boost the team: "I think the team on Friday night will be bolstered by having Stephen back in the squad, he does make a big difference.
"Ulster will be in a good frame of mind leading into this game and I think it's an important game for both teams as we approach Europe. The conditions up there are often difficult and the crowds are very hostile, but these environments are one of the reasons why you play rugby and I think some of the young guys will really relish that and hopefully we can get a good victory.
"Every Magners League game is important but this game becomes important from a points point of view, and icing on the cake will be that extra bit of confidence a win will give us going into the Heineken Cup."
Meet the members of the WRU's inaugural Youth Board - after an online selection process which saw a host of high calibre candidates submit video applications the WRU has made its first 15 appointments.The board is made up of individuals aged between 16 and 21, and will meet for the first time at Principality Stadium on Monday 15th February.
The Wales Women's team headed to Dare Valley Country Park on a team bonding exercise as the entire squad got together for the very first time in preparation for this season's Six Nations championship which kicks off on Saturday with a clash against defending champions Ireland, in Donnybrook.
Wales Head Coach Warren Gatland discusses his team selection for the opening round of the RBS 6 Nations where he leads his side against Ireland, on Sunday. As WRU TV's Luke Brodley discovers, Gatland is fully aware of the challenges the defending champions pose