The Austrian, who won the first World Cup event of the season, picked up his second-ever World Cup win as he finished 25.6 seconds clear of Germany's Fabian Reissle.
Franz-Josef Rehrl, who had won the first two events of the Triple, was third, but it was his compatriot Seidl who claimed the three-day crown.
Overall World Cup leader Jarl Magnus Riiber of Norway came home in fifth but saw his advantage at the top of the standings cut by Seidl.
Riiber leads the way with 858 points, with Seidl now up to second with 669 points and Germany's Johannes Rydzek in third (648).
Day 5, Sheffield