Fresh from his maiden win in the 5km Individual Gundersen on Friday, the Austrian finished 24.3s clear of Japan's Akito Watabe following the ski jumping and a 10km race.
Watabe nudged out Germany's Fabian Riessle for second by just 0.5s, while Norway's Espen Bjoernstad was only 0.4s off the podium in a frantic finish to the race.
But out front Rehrl was in firm control after his 117.5m jump gave him a 45s advantage before the 10km, which he finished in 22m58.7s.
He now moves fifth in the overall World Cup standings, with Norway's Jarl Magnus Riiber still comfortably out in front.
Brands Hatch, 2016
Day 5, Sheffield