The Saints added the Super League title to their haul of the Powergen Challenge Cup and the league winners shield with another professional performance.
After being fortunate to lead 10-4 at half time, Daniel Anderson's side ran in three unanswered tries to be crowned champions for a fifth time in the Super League era.
Full-back Paul Wellens capped a memorable week by claiming the Harry Sunderland Trophy as man of the match after being named Man of Steel on Monday.
Although Hull played their part in a gripping contest, their inability to make the most of their chances cost them dear.
In contrast, Saints showed they had the killer instinct in attack, typified by Leon Pryce's try that gave them a crucial half-time advantage.
The former Bradford man's clever dummy, coupled with an excellent hand-off, sent him through down the left to go over in the corner.
His solo effort came straight after Hull had wasted a great opportunity to score themselves when they had been called for obstruction on the first tackle after a penalty for a high shot.
It also pushed Saints' noses in front, despite the fact they had spent much of the opening half on the back foot.
Playing for just the second time in a month, Saints looked rusty in the opening exchanges against a Hull unit that showed no signs of nerves in their first ever Grand Final.
Gareth Raynor came close to breaking the deadlock but he was just forced into touch after Paul Cooke's long pass had given the winger a clear sight of the line.
However, Hull were unable to yield any points from their early pressure and they paid the price for their profligacy as they were hit with a sucker punch.
After gaining excellent field position following a penalty, Sean Long's well-weighted kick allowed Francis Meli to slide over for the first try of the night.
To their credit, Hull bounced back off the canvas to score an excellent try of their own.
Cooke's bomb out to the right wing was well taken by Motu Tony, who managed to offload the ball to allow Sid Domic to squeeze over.
It took Pryce's moment of magic to separate the sides at the interval and that advantage was soon extended with a quick-fire double at the start of second half.
Willie Talau benefited from some slick passing to go over on the left and that was followed up by a try for Ade Gardner as he rose highest to beat Raynor to Long's high kick into the corner.
Hull bravely tried their best to produce a comeback, but their desperation to find a way through led to mistakes.
Keiron Cunningham - who had needed to pass a late fitness test to play - made them pay for one error, barging his way over from close range.
The hooker's try was the knockout blow for Hull, who came up just short in their efforts against a Saints side that have been simply the best in Super League XI.
Engage Super League Grand Final Old Trafford St Helens (10) 26. Tries: Meli, Pryce, Talau, Gardner, Cunningham. Goals: Lyon 3.
Hull (4) 4.