The winger scored two tries tonight to help deliver his side the Super League title and ensure Warrington’s long wait for a championship goes on.
But Manfredi came close to quitting the sport after missing two years of action due to two serious knee injuries.
He only finally made his return against Warrington last month but came up with the crucial plays this evening in what was a tense but mistake-ridden showpiece.
Manfredi scored in the first half and produced a try-saving tackle on Tom Lineham in the second period that saw him need to leave the field with a nasty head wound.
However, he returned, bandaged up, and, with the game still hanging in the balance - no team had added to the 8-4 interval scoreline - the 25-year-old dived in for his second in the 76th minute.
It meant, in front of a crowd of 64,892, Wigan head coach Shaun Wane got his perfect send-off in his last game in charge before leaving to join Scotland Rugby.
Wigan trio Sam Tomkins, who heads to Catalans, and Canberra Raiders-bound John Bateman and Ryan Sutton, also signed off in style.
However, full-back Tomkins was lucky to still be on the pitch to produce the pass for Manfredi’s second after two unsavoury first-half incidents.
First, he blatantly tripped Bryson Goodwin as the Warrington centre cleared up a loose ball.
Referee Robert Hicks could easily have handed the full-back a yellow card but merely spoke to him and awarded a penalty.
Later, though, Tomkins slid in and kneed Daryl Clark in the head as the Warrington hooker - and England team-mate in the weeks ahead - went to ground.
Again, the Wigan player could have had no arguments with a sin-binning - or maybe more - but again Hicks kept his cards in his pocket.
The game threatened to boil over at that point and players were seen scuffling in the tunnel as they headed off at half-time.
Warrington had opened the scoring with former Wigan winger Josh Charnley crossing in the 14th minute.
However, they would not score again and were left to rue a raft of handling mistakes - it was a scrappy final - that meant they wasted plenty of prime attacking positions.
Wolves full-back Stefan Ratchford was a threat, making a couple of breaks in the second period and winning the Harry Sunderland Award as man-of-the-match, but time after time his side lacked a finishing touch.
Favourites Wigan defended well but Warrington - who also lost the Challenge Cup final at Wembley and have not won the league since 1955 - will realise they did not ask enough questions.
Manfredi scored his first in the 26th minute after some quality play from Oliver Gildart, the young centre last week called up to the England squad.
Fellow winger Tom Davies then put Wigan ahead when he latched on to George Williams’ grubber in the 31st minute and it would prove enough, even with Tomkins missing all his conversion attempts and a penalty.
It is the third time Wigan have beaten Warrington in the Grand Final having also done so in 2013 and two years ago.
Wigan Warriors: Tomkins; Manfredi, Gildart, Sarginson, Davies; Williams, Leuluai; Navarrete, Powell, Flower, Greenwood, Bateman, O’Loughlin. Substitutes: Escare, Sutton, Farrell, Clubb.
Warrington Wolves: Ratchford; Lineham, Goodwin, T King, Charnley; Brown, Roberts; Hill, Clark, Cooper, Thompson, Hughes, Westwood. Substitutes: Philbin, Murdoch-Masila, G King, Patton.
Referee: Robert Hicks (Oldham)