William was sheriff of Forfar (1195–1211), Justiciar of Scotia (1205–1233) and warden of Moray (1211–12).
From 1195 to 1211, William held the position of sheriff in Forfar. From 1205 to 1233, he served as Justiciar of Scotia. Finally, from 1211 to 12, he was warden of Moray.