Pep Guardiola's men fell behind to a Seagulls' set piece in the first half, but hit back straight away, edged ahead and eventually coasted home with two further goals after the break.
It is a remarkable achievement from a quite remarkable team and it is the closing chapter on an unforgettable title race.
In brilliant sunshine at a resplendent Amex Stadium, City strode out to try and finish a job that has been 10 months in the making.
Bernardo tried to get the Blues off to the perfect start with a run that saw him weave through a couple of challenges before foiled as he was about to pull the trigger.
The hosts had set their stall out, defending deep and in numbers every time City attacked, while occasionally breaking forward themselves.
It was nervy stuff from Guardiola's side who were struggling to make an impact on the Brighton goal, and when news came through that Liverpool had scored against Wolves, so the tension cranked up another notch.
But if that was agonising for the watching and listening fans, on 27 minutes, things got much worse as a Brighton corner was poorly defended, and Glenn Murray nodded home from two yards out.
Suddenly, in the ‘as it stands’ table, City were now two points adrift of Liverpool – but the goal acted as a huge wake-up call and the response was immediate.
Aymeric Laporte played a low ball to David Silva whose flick ran perfectly for Aguero who buried a low shot past Matt Ryan to level the scores.
Just 83 seconds of pain, then!
City were suddenly alive, the movement better and the urgency visible for all to see.
Brighton were rocking slightly and on 38 minutes, we finally had the lead as Mahrez’s corner was powerfully headed down and into the roof the net by Laporte.
We had one hand on the Premier League trophy with the travelling fans going through the full gamut of emotions in that first 45 minutes.
Just another 45 to go…
City stroked the ball around nicely in the warm Sussex sunshine, looking for the goal that would allow some much-needed breathing space.
It was patient and precise and on 63 minutes a moment of brilliance that put City 3-1 up.
David Silva saw the lurking Mahrez slightly ahead of him, played a short pass to the Algerian who sold an outrageous dummy on the edge of the box before unleashing a right foot howitzer into the top corner to send the travelling fans wild.
Eight minutes later and the game was over as provided the icing on the cake with a 25-yard free-kick into the top right-hand corner to give the Blues an unassailable 4-1 lead.
And that was that as the champions comfortably saw out the minutes that remained to claim a second successive Premier League title.
Drama to the last
For 10 painful minutes, it was the scenario we all dreaded – Liverpool ahead and City behind.
Many pundits had predicted the Merseysiders would go top at some stage in the final day and after 17 minutes at Anfield, that prophecy had come true.
At that moment, Liverpool led the Premier League by a point – and 10 minutes later when Brighton scored, it was a two-point lead.
But in a title race where the lead had changed hands 32 times, within the next 10 minutes it was City who again led the live table.
What it means…
City are champions and have now won three domestic honours this season.
The Blues finish one point ahead of Liverpool, who beat Wolves 2-0 at Anfield to add to the FA Community Shield secured in August and the Carabao Cup which was lifted after a dramatic penalty shoot-out with Chelsea.
Today's superb win ends an epic title race in which both sides swapped places on an almost weekly basis and now only Watford stand between City becoming the first team to win all four English trophies in the same season.
Next week's FA Cup final has plenty riding on it!
Star man: Riyad Mahrez
An excellent decision to play Mahrez by the boss and the Algerian repaid his manager’s faith with a stellar display, a goal and an assist.
City round off an unforgettable campaign with the FA Cup final against Watford at Wembley next Saturday afternoon.