The 29-year-old has joined the Club on a free transfer after his contract at Arminia Bielefeld expired.
The experienced German bolsters City’s goalkeeping options and becomes the second signing of the summer, following Erling Haaland to the Club. He will wear the number 18 shirt.
The move is subject to international clearance ahead of him joining up with the squad this month ahead of preseason.
Ortega Moreno says the chance to join City was an opportunity he could not miss.
“This is a fantastic move for me,” he said. “Manchester City are an amazing team – a squad with world-class quality in every area. To be given the chance to join this group of players and help continue the Club’s success is a dream for me.
“I have enjoyed my time in Germany and I want to thank the Arminia Bielefeld fans for their support. But this new challenge of coming to City and playing in the Premier League is too good for me to ignore.
“I can’t wait to get started, meet my teammates and begin working with Pep and his backroom staff.”
Director of Football Txiki Begiristain added: “This is a very good deal for City.
“Stefan has excellent pedigree – his career speaks for itself.
“We are signing a goalkeeper who has vast experience, and he will help us in our quest for more trophies.
“He has joined to compete with the other goalkeepers and help our youngsters, so it’s a transfer we are really pleased to have secured.”
Ortega Moreno started all but one of Arminia Bielefeld’s Bundesliga matches last term.
In total, he made 220 appearances across two different spells at a team he joined as a youngster in 2007. He made his first-team debut four years later, helping them win promotion to 2. Bundesliga in 2013.
He joined TSV 1860 Munich in 2014, making 64 appearances in three years there, before re-signing for Arminia Bielefeld in 2017 and eventually becoming vice captain.
Everyone at City welcomes Stefan to the club and we wish him all the very best during his time here.