treby was the only son of james treby and the nephew of sir george treby, lorg chief justice. he joined the army and was a lieutenant in colonel roger townshend’s foot in april 1706. he was captain in. colonel de magny’s portuguese regiment of foot in 1709, and captain in the 10th dragoon guards in 1715. in january 1720 he became captain and lieutenant-colonel in the 1st foot guards and then reserve captain when he became governor of dartmouth castle in the same year.