portman was the son of john portman, who was buried in the temple church on 5 june 1521, by alice, daughter of william knoell of dorset. his family was long established in somerset, having given its name to the former manor and present village of orchard portman, and he served as justice of the peace for that county from time to time. he was a barrister who was successful enough to be personally known to king henry viii. in 1532 he acquired 270 acres adjacent to the nw of the city of london, which estate stretching from today's oxford street to the regents canal, known as the portman estate, is still held by his descendants the viscounts portman. in 1533 henry viii gave him a wardship, and he was one of the administrators of the will of catherine of aragon.