Arsenal, who enjoyed an eight-point lead over City as recently as mid-March, needed at least a point to stay mathematically in the hunt, but went down 1-0.
City, who host Chelsea on Sunday, have 85 points with three games to play, while Arsenal are on 81 with one game left.
It is City's seventh Premier League title since they were bought by Abu Dhabi's Sheikh Mansour bin Zayed Al Nahyan in 2008 and they are now just two wins away from completing a treble only previously achieve by Manchester United in 1999.
City face Manchester United in the FA Cup final on June 3rd and a week later take on Inter Milan in the Champions League final - starting big favourites in both games.
While Arsenal have threatened to knock City off their perch this season, it all proved an illusion in the end as Pep Guardiola's side again proved relentless in the run-in.
Since losing to Tottenham Hotspur on February 5th they have taken 40 points from the next 42 on offer and have won their last 11 matches. They have also comprehensively beaten Arsenal home and away.
If City win their last three games they will reach 94 points, not as many as the totals they achieved in 2017-18 and 2018-19, Guardiola's first two league titles.
But the way they have finished the season suggests the gap between them and the rest is widening.
Club captain Ilkay Gundogan (32) described the latest title as something "very special".
"The Premier League is without doubt the most demanding and competitive league in the world so that tells you everything about what an achievement this is," he said.
"This squad is so talented and so special and to have been captain this season has been an enormous privilege.
"To have won this trophy three times in a row and five times in six years is incredible. That quality and consistency helps sum up what Manchester City stand for and ensures the club will continue to strive for success going forward."
Arsenal will have to be content with the runners-up spot and a return to the Champions League after a five-year absence.
But manager Mikel Arteta (41) will have much to ponder as he analyses how the Gunners buckled under City's relentless pressure. Defeat at Forest means Arsenal have won only two of their last eight matches in the league.
