Knowing only a final day victory could guarantee glory at the expense of Jurgen Klopp's relentless Liverpool, Pep Guardiola's men were stunned by a 27th-minute Glenn Murray opener.
Final-day specialist Sergio Aguero found a response within 83 seconds and Aymeric Laporte converted Riyad Mahrez's 38th-minute corner to put City back in control of their destiny.
Mahrez, a surprise selection after an underwhelming debut season at the Etihad Stadium, made good on his record-signing status and Ilkay Gundogan added further gloss for the raucous travelling supporters who have now seen their team prevail in four of the past eight Premier League seasons.
City were far from their fluent best early on and, after the Albion faithful merrily relayed news of Sadio Mane's 17th-minute opener against Wolves in an eventual 2-0 win at Anfield, they fell behind.
Murray found himself on the right end of a mismatch with Oleksandr Zinchenko when he converted Pascal Gross' corner at the near post.
The response was instant and clinical, with Aguero drilling David Silva's delightful flick through the legs of Mat Ryan.
Brighton's goalkeeper then denied Bernardo Silva and Mahrez but erred in letting the latter save dribble behind. Laporte rose gleefully to power in Mahrez's looping delivery.
A rasping Gundogan drive after half-time failed to penetrate a mass of bodies, although Ryan did not do the efforts of those in front of him justice in the 64th minute.
Mahrez deftly sashayed into space but found the ball on his weaker right-foot. The winger struck his speculative effort well, but Ryan should have done better than slapping into his top corner.
The Australia international was helpless 18 minutes from time as Gundogan – possibly on a farewell appearance for City as a new contract remains unsigned – curled in a majestic free-kick to get the party started.
What does it mean? Guardiola cements his legacy as City eye dominance
Last season's 100-point procession saw City break records but it was a largely pressure-free exercise. This time around, it is hard to imagine greater scrutiny than that supplied by Liverpool, with 98 points besting 97 in an echo of Guardiola's unforgettable tussles with Real Madrid while at Barcelona. City are the first team to retain the Premier League since Alex Ferguson's Manchester United did so in 2008-09. With Guardiola at the wheel, a similarly dominant period could be in prospect on the other side of Manchester.
Aguero thrives under final-day pressure yet again
Not a moment that will quite rank alongside his last-gasp heroics against QPR in 2012, but City's day might have unravelled without Aguero's expertly dispatched equaliser. Guardiola's team failed to fire before falling behind, with the latest manifestation of the near on-field telepathy enjoyed between David Silva and Aguero coming at the perfect moment.
Murray undoes his good work
There has been a social media trend among Liverpool supporters over recent weeks of changing their online avatar to a picture of whatever striker was next in line to try to derail City's title defence. Where Ashley Barnes and Jamie Vardy failed, Murray succeeded by giving Brighton the lead. However, he gave away possession for the quickfire equaliser and afforded Laporte the freedom of Sussex for City's crucial second.
Key Opta facts
8 - This was the eighth time the Premier League title has been decided on the final day of the season, with Manchester City winning it on three of those occasions (2011-12, 2013-14 and 2018-19). Finale. pic.twitter.com/tpLE4ytySl— OptaJoe (@OptaJoe) May 12, 2019
- Manchester City have won their fourth Premier League title – only Manchester United (13) and Chelsea (5) have ever won more in the competition.
- Overall, Manchester City have won their sixth English top-flight title. They’re the first side to retain the title since Manchester United in 2008-09.
- Manchester City’s haul of 98 points is the joint-second highest for any team in English top-flight history (converting to three points for a win) – only the Citizens themselves have ever earned more (100 in 2017-18).
- Manchester City conceded the first goal in a Premier League game for the first time since their 0-2 defeat at Chelsea in December – they were behind for just 83 seconds before Sergio Aguero’s equaliser.
- Manchester City have won their last 14 Premier League games – only the Citizens themselves (18 in December 2017) have had a longer winning run in the competition.
- Manchester City have won 32 Premier League games this season – equalling their own record in the competition from last season for most wins in a single campaign in the competition.
- Sergio Aguero has scored 32 goals in all competitions for Man City this season – only in 2016-17 (33) has he scored more in a single campaign for the Citizens.
- Man City’s David Silva has provided 18 assists for Sergio Aguero in the Premier League – only three players have ever assisted another for more goals in the competition (Frank Lampard to Didier Drogba, Darren Anderton to Teddy Sheringham and Steve McManaman to Robbie Fowler).
- Glenn Murray has scored 36% of Brighton’s overall Premier League goals (25/69), the highest proportion of any team’s goals in the competition’s history.
City pursue an unprecedented domestic treble when they face Watford in next weekend's FA Cup final, while Brighton face a close season of reflection and reassessment. They avoided relegation but closed their Premier League campaign with a run of nine winless matches.