Tengku Mahmud was married to Tengku Ampuan Bariah, the Selangor Royalty.
His second marriage with Sharifah Nong Fatima binti Sayyid Abdullah, the mother of the current Sultan of Terengganu, Sultan Mizan Zainal Abidin.
Tengku Mahmud ascended the throne as Sultan Mahmud al-Muktafi Billah Shah on 20th September 1979. His installation was held on 21st March 1981 at the Maziah Palace.
Sultan Mahmud died in Singapore on 14th May 1998 and was laid to the rest in the Royal Mausoleum in Kuala Terengganu on 15 May 1998