The victory marks Littler's first World Series triumph of 2025, adding £30,000 to his growing haul of the season's prize money.
From the outset, Warrington's favourite son imposed himself.
A break of throw in the second leg set the tone, followed by a sequence of heavy scoring that included back-to-back 180s in the sixth leg.
That left him on 45 after just nine darts, cleaned up in two for a 4-2 lead.
The Nuke finished the match having hit seven 180s, an eye-catching 143 checkout, and a 174 visit that set up the winning double.
De Decker, who had impressed throughout the week by defeating world number one Luke Humphries in the semi-final, refused to roll over. He claimed legs with 13-dart holds and produced a tidy 57 finish when requiring 146.
At 6-4 down, he still had faint hopes, but Littler’s 12-dart hold in the 11th leg effectively ended the contest, leaving De Decker needing four straight legs to stay alive.
While Littler's finishing on double 16 briefly deserted him - he missed six darts at it in one leg - his checkout accuracy elsewhere was decisive.
A 103 attempt fell narrowly short, but he compensated with clinical shots at double 10, double five and bullseye, including an 81 finish under pressure.
Littler averaged 98.69 to De Decker's 89.66, with both hovering around 50 per cent on the doubles.
The win adds another title to Littler's already impressive 2025 campaign, which includes the World Championship, UK Open and World Matchplay.
Humphries whitewashed
Earlier in the evening, world number one Humphries suffered a shock whitewash against eventual runner-up De Decker in the quarter-finals - just the third legless match in his illustrious career - with the world number 19 averaging 103.66 and hitting 46 per cent of his doubles.
Northern Ireland's Josh Rock also suffered the same mauling at the hands of Stephen Bunting, while Chris Dobey also got one over Gerwyn Price with an impressive 6-4 victory before falling to a 7-4 defeat to the Belgian in the semis.
Littler would dispatch Bunting 7-4 in a high-quality semi-final, with both over 50 per cent on the doubles.
The 18-year-old takes home £30,000 in prize money, while De Decker receives £16,000 as runner-up.
The PDC now heads to Auckland next week for the New Zealand Darts Masters.