The Reds have cruised to the title - their first in 30 years - but showed signs of a hangover from the midweek trophy celebrations as they trailed to Dwight Gayle's first-minute opener.
Although Mohamed Salah, Sadio Mane and Roberto Firmino all started from the bench, Jurgen Klopp's men recovered to turn the game on its head either side of half-time.
Virgil van Dijk equalised and Divock Origi then grabbed his first goal since December before Sadio Mane added late gloss to the scoreline as Liverpool finished the campaign with 99 points, its best ever top-flight haul and only one shy of Manchester City's 2017-2018 record.
The surprise Gayle goal had seen Newcastle lead Liverpool early for the second time this season, with his 25-second effort the fastest the Reds have ever conceded in the Premier League.
Allan Saint-Maximin quickly won a foul on halfway and Jonjo Shelvey's free-kick sent Gayle clear to stab past Alisson, prompting a lengthy VAR review for a potential offside before the goal was given.
Liverpool's subsequent dominance initially spawned only a speculative Takumi Minamino effort, which Martin Dubravka saved well, before Alisson had to be alert to field an unorthodox Federico Fernandez drive at the other end.
But with the Reds' usual attacking stars watching on, Van Dijk stepped up and looped a towering header over Dubravka from Alex Oxlade-Chamberlain's right-wing cross.
Klopp readied Salah, Mane and Firmino as Liverpool made a slow start to the second half, yet the imminent changes provoked Origi to blast in the visitor's second, his shot passing through a crowd of bodies to deceive Dubravka and pick out the bottom-right corner.
The triple substitution followed regardless and Salah's first involvement saw a powerful strike bounce off the post, but it was Mane who provided the final flourish.
Cutting inside from the left in trademark fashion, the winger curled beyond Dubravka to end Liverpool's season in style.