Tuanku Sallehuddin was born (as Tunku Mahmud Sallehuddin) and raised in Istana Anak Bukit, Alor Setar, Kedah.[2] He was the ninth of 14 siblings, to Sultan Badlishah, the 27th Sultan of Kedah, and Sultanah Asma, daughter of Sultan Sulaiman of Terengganu.