The 34-year-old spent the 2016-17 season at the Etihad Stadium without making a single first-team appearance before eventually rebuilding his career in Spain and the Netherlands, and he now returns on a two-year deal reported at £1.7 million as understudy to number one Gianluigi Donnarumma.
The move fills the gap left by James Trafford's departure to Leeds United in a deal worth up to £45 million, with Rulli identified as Manchester City's preferred option for a settled, experienced deputy rather than another developing young goalkeeper.
"This is an amazing opportunity for me and one I had to grasp. When the chance to join Manchester City comes along you have to go for it," Rulli said.
"Everyone knows what an impressive club this is. City's success over a long time has been impressive.
"Everyone I have spoken to about City said I had to join them because they are a club with incredibly high standards. Every professional wants to be in a high-performance environment and I can't wait to get started because I know I will improve and learn, which is always my main priority."
Between his two spells at City, Rulli built a decorated career across four countries, winning the Europa League with Villarreal in 2021 in one of the competition's most dramatic finals, when he scored in the shootout before denying opposite number David de Gea to seal victory over Manchester United. He went on to play for Ajax and, most recently, Marseille, and won both the 2022 World Cup and the 2024 Copa America with Argentina during that period, in addition to reaching this summer's World Cup final with his country.
Rulli becomes City's third summer signing since Enzo Maresca's appointment as manager ahead of the 2026-27 campaign, and he is looking forward to working with fellow Argentine Willy Caballero, who joins goalkeeping coach Michele De Bernardin on Maresca's backroom staff.
"It means a lot to have Caballero at City. Because he's Argentinian, also a goalkeeper and we have some things in common. It will be really nice to share the day-by-day with him," Rulli said.
He also credited his conversation with De Bernardin as central to making up his mind about the move.
"When I spoke with Michele, the goalkeeper coach also, it was an easy decision to come. I also saw the team when he was at Chelsea, I really liked the style and how they prepare the games. In this moment I can't wait to start with the team. To help and to win."