Kolisi began his career with the Stormers and captained the side before leaving for French side Racing 92 in France and later joining the Durban-based Sharks.
The two-time Rugby World Cup winner is one of the most iconic players in the game and the most successful Springbok captain, who will be 35 by the time he makes the move for the start of the 2026/27 season.
He is hoping to lead the Springboks at a third successive World Cup in Australia in 2027, but also has a desire to be closer to his family in Cape Town.
His professional rugby journey started in Cape Town after he left school and he is now poised to add to his 118 Stormers caps.
“I have such incredible memories of my time at the DHL Stormers, the way I was embraced by the fans in my formative years has never left me,” Kolisi said.
“My family is in Cape Town and it is important to me to be close to them. This move gives me the chance to do that while also giving back to the team and fans who made such a big contribution to the player and person I am today.
“I am looking forward to contributing in any way I can to the future success and happiness of this special club and its incredible supporters,” he said.
Director of Rugby John Dobson said that Kolisi will add value to the squad in ways that no other player could.
“We have got an outstanding crop of loose forwards in our squad and a number of very strong young leaders, with the last three Junior Springbok captains all on our books,” Dobson said.
“Siya will be able to help develop these players and mentor them in a way that nobody else could, given what he has achieved and what he represents to all South Africans and especially our fans.
“We are very aware of the load that he has carried professionally and personally over the last few years, but what is so encouraging is the way that he has bought into helping us reach the goals we have set for ourselves in developing our squad as we build towards Project 2029.”
The Stormers have made an unbeaten start to their 2025/26 season with seven wins out of seven in the United Rugby Championship and two from two in the European Champions Cup.