The win lifts Wigan into top spot at the expense of St Helens who take on London Broncos on Sunday, while Castleford slipped to a 10th league defeat of the season.
Soon after he had broken the deadlock with seven minutes gone, Marshall touched down again for Wigan, but it was chalked off for a knock-on.
Hoy’s try, just past the half-hour mark, was against the run of play and came from deep in Castleford’s own half.
The full-back picked the ball up and showed great speed to exploit a gap in the Wigan defence, dummying Bevan French along the way before crossing.
Cas raced out of the blocks after the break and edged ahead courtesy of Milnes’ penalty, but they were reduced to 12 men soon after.
Cain Robb was sent to the bin for a high tackle on Wigan’s Abbas Miski but Cas added to their lead despite the numerical disadvantage, with Milnes on target from long range.
The lead did not last long, however, as Jake Wardle’s last-ditch offload was deflected by Milnes into the path of Marshall who reacted fast to dot down.
Harry Smith missed the conversion attempt with the match still finely poised at 8-8 but he hit the target with a penalty moments later to edge Wigan in front.
It proved decisive and, despite Castleford’s best efforts in the closing stages, they could not breach the Wigan back line to register what would have been a well-deserved victory.
