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."
GB7s women left their England base to train in Wales this week. Olympic Games hopeful Rachael Burford gives WRU TV's Graeme Gillespie her thoughts on Welsh teammate Jasmine Joyce - a 'one touch wonder'
The GB7s women's squad is currently training at Wales' Centre of Excellence where assistant coach Richie Pugh tells WRU TV's Graeme Gillespie some 'tough calls' will have to be made when it comes to finalising the 12 spots for Rio's Olympic Games.
Wales U20's Billy McBryde is looking forward to starting his first game against New Zealand this afternoon in the World Rugby U20 Championship where his side are looking to gain revenge from last week's pool defeat to the Kiwis.