The Saints were crowned champions of the English-based Super League for the first time since 2006, coming out on top after losing their previous five Grand Finals.
Soliola, who will join the Canberra Raiders in Australia's NRL next year after five seasons at Langtree Park, had himself been involved in two of those Grand Final defeats during his time in north-west England.
But it was third time lucky for the 28-year-old, although St Helens were made to work desperately hard by their Lancashire rivals, despite defending champions Wigan playing most of the match a man down after prop Ben Flower was sent off in the second minute for punching.
Nevertheless, Wigan led 6-2 at half-time thanks to winger Joe Burgess' try.
However, Soliola bundled his way over early in the second half before Tommy Makinson's try secured a 14-6 victory that was also the perfect farewell present for Saints coach Nathan Brown, returning to Australia for family reasons.
Wigan got the first points of the contest in the 16th minute.
St Helens were penalised for obstruction in their own half as wing Adam Swift tried to break, and Matty Smith bisected the posts from 25 metres out.
There was no let-up from Wigan but a stoic St Helens defence was able to hold out.
And their reward came after 29 minutes when Mark Percival equalised with a straightforward penalty.
With the clock ticking down to half-time, Wigan wing Burgess grabbed the game's first try, finding space following a pass from Melbourne Storm-bound half-back Blake Green to slide into the corner.
Smith missed the touchline conversion.
Wigan stifled a handful of early second-half attacks but they could not prevent Soliola from burrowing over the line in the 53rd minute, with Percival landing the easy conversion.
With 12 minutes remaining, and the next score seemingly vital, Makinson delivered the decisive blow for Saints.
Rising high above Bowen and Smith, the winger claimed Paul Wellens's up-and-under to ground the ball and stretch the Saints' lead before Percival goalled again.
-AAP
