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."
Angus O'Brien has quickly settled into the Wales Sevens squad after solid performances in Hong Kong and Japan. With two rounds remaining in Glasgow and Twickenham on the World Series, WRU TV's Graeme Gillespie chats to the rising star.
Wales winger Luke Morgan has established himself as one of the deadliest finishers on the Sevens World Series. WRU TV's Graeme Gillespie catches up with him on the eve of this weekend's round in Glasgow.
All roads lead to Cardiff on Sunday for the SSE SWALEC Finals Day at the Millennium Stadium. Cambrian Welfare tackle Ystradgynlais in the Bowl final, Ystrad Rhondda play Newcastle Emlyn in the Plate final while defending champions Pontypridd face Bridgend in the Cup final.
WRU Chief Executive Roger Lewis, Deputy Minister for Culture, Sport and Tourism Ken Skates and WRU Chairman Gareth Davies earlier this week launched a new competition in conjunction with the WRU unveiling its archive room.
Welsh players and management joined Deputy Minister for Sport Ken Skates at the Pierhead Building, Cardiff Bay earlier this week to reveal the Union's pioneering school-club hub initiative has been so successful the project will now almost double the scale of the original project.
The Scarlets, Newport Gwent Dragons, Cardiff Blues and the Ospreys look ahead to Judgement Day III which sees the Blues take on the Ospreys (2.30) and the Dragons tackle the Scarlets (4.45pm) at the Millennium Stadium tomorrow afternoon.
Ystradgynlais and Ynysddu played out a titanic struggle at Taffs Well in the SSE SWALEC Bowl semi-final. At the end of the game neither team could be separated after a 15-15 stalemate but Ystradgynlais go through on try count.
Blues strike first in JD III battle - Newport Gwent Dragons lock Andrew Coombs, WRU referee Dylan Llyr Jones and Cardiff Blues hooker Matthew Rees decide dressing room allocations for Judgement Day III
Wales Under 18 captain Calum Haggett has received a conditional offer to read Biomedical Science at St Anne's College, Oxford. WRU chairman Gareth Davies went to meet Calum and Coleg y Cymoedd Principal Judith Evans to wish him luck in his exams and pass on some of his personal experience.