Pryce scored a vital try for Saints before the interval
St Helens: (10) 26
Tries: Meli, Pryce, Talau, Gardner, Cunningham.
Goals: Lyon (3)
Hull: (4) 4
Two tries in four minutes earned St Helens a Challenge Cup, minor Premiership and Grand Final treble but only after brave resistance from Hull.
Sean Long's kick set up Francis Meli's opener before Sid Domic finished off a slick move to level for Hull.
Leon Pryce's score put daylight between the teams at half-time before Willie Talau and Ade Gardner turned the screw.
By the time Keiron Cunningham scored his 150th try for Saints, the outcome was already a formality.
Although Saints drew first blood, it was only after they had endured an early battering from Hull.
Gareth Raynor looked to have put them ahead when he went over in the corner, but a superb last-ditch tackle by Jamie Lyon put him in touch as went over, and the try was not given.
When the opening try came, it was a result of Meli spotting Motu Tony out of position, and an inch-perfect kick by Long which bounced perfectly for him to touch down.
But Hull's equaliser from Domic came at the end of a spectacular move, begun when Shaun Briscoe was put through superbly by Richard Swain, only to be denied by Jon Wilkin's tackle.
From the resulting play-the-ball, Paul Cooke put a high ball in the corner, which was taken by Tony, who offloaded to Shayne McMenemy, whose pass set up Domic to score.
Hull did not let up as the half wore on, but in the dying seconds, they were penalised for obstruction, and from the turnover Pryce sprinted 30 metres into the corner to score, with Lyon adding the goal.
A double strike by Talau and Gardner shortly after the restart broke Hull's resistance.
Talau finished off a passing move while Gardner converted another Long high ball, and there was no way Hull could recover.
Cunningham made light of a midweek illness to add St Helens' fifth try and although both teams continued to give their all, Saints' triumph was never in question.
The former Great Britain international's try was converted by Lyon, who scored three goals in his final appearance for Saints before his return to Australia.
Saints full-back Paul Wellens capped the best week of his career with the Harry Sunderland Trophy for man of the match coming hot on the heels of his Man of Steel honour.
The match was also a fitting farewell for veteran prop Paul Anderson, who hung up his boots after collecting a third Super League ring on a record-equalling sixth Grand Final appearance.
St Helens: Wellens, Gardner, Lyon, Talau, Meli, Pryce, Long, P. Anderson, Cunningham, Cayless, Gilmour, Wilkin, Hooper. Replacements: Roby, Graham, Bennett, Fa'asavalu.
Hull FC: Briscoe, Tony, Domic, Yeaman, Raynor, Cooke, R. Horne, Dowes, Swain, Carvell, McMenemy, Radford, Washbrook. Replacements: Whiting, G. Horne, Wheeldon, King.