The Algeria worldwide, one of Leicester's title-winning heroes from the 2015-16 season, handed in a transfer request in January and had a 10-day absence from the club before returning to training with them on February 9.
Whilst Cristiano Ronaldo's switch to Juventus took most of Tuesday's headlines, the Premier League champions unveiled the Algerian worldwide late in the evening.
"I am very happy to have signed for City, a team that plays great football under Guardiola", said Mahrez, a Premier League victor with Leicester.
'Watching them from afar has been a pleasure. "Pep is committed to playing attacking football, which is a flawless for me, and City's performances last season were outstanding", he said on the club's official website.
"I believe my own game can develop under Pep's management".
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"Riyad is a hugely talented player", Begiristain told the official Man City website.
Manchester City signing Riyad Mahrez. "He beats defenders and creates space", he said.
Mahrez will go down as one of the bargains of the Premier League era, having joined Leicester for a reported 400,000 pounds (now $530,000) from French club Le Havre in 2014. "We're sure he will bring additional attacking quality to our squad".
The Foxes also are better prepared for him to leave this time as they bought highly-rated James Maddison from second-tier Norwich City for £2 million earlier in the close season.
Interestingly, the Algerian was back in Leicester's good books as he netted four more goals for the Foxes, taking his total goals to 39 goals from 139 top flight games for the King Power dwellers.