In 1910, Tunku Ismail, accompanied by Onn Jaafar, returned to Johor and spent three years in Perak, where they enrolled into the Malay College Kuala Kangsar.

[3] In 1937, Tunku Ismail appointed Onn Jaafar by this point a state executive councillor, as his private secretary and entrusted him to run the Johor Pavilion at the world fair in San Francisco the following year.

[5] Tunku Ismail returned to Johor after the war and was confronted with Malay nationalist movements which had erupted as a result of the rulers' dissatisfaction with the Malayan Union scheme.

[6] Nevertheless, Tunku Ismail officiated the opening ceremony of the United Malays National Organisation's (UMNO) first congress which was held at the Istana Besar in May 1946 while Sultan Ibrahim was residing in London.

[9][10] The Sultan was known to be very close to his subjects; he made annual trips to visit selected villages in the eight districts of Johor and frequently acquainted himself with the civil servants working for the state government.

While his wife was permanently left in a vegetative state until her death a month later owing to brain damage, the Sultan survived with only minor injuries.

[21] Sultan Ismail died on 10 May 1981 at 6:12 pm at the Royal Ward Hospital Besar, Johor Bahru after being admitted two weeks earlier following an illness at the age 86.

His death was only officially announced at 8:45 pm by Menteri Besar of Johor Tan Sri Dato' Haji Othman Saat.