Tun Mohd Hamdan was born on 22 February 1922 at Kampung Labuaya, Tuaran, British North Borneo.
[3] Tun Mohd Hamdan firstly married Toh Puan Selisir binti Judi, who was also an ethnic Lotud Dusun.
[4] In 1962, Tun Mohd Hamdan married a second wife, Toh Puan Dulimah binti Ampit, also a Lotud Dusun but a fellow Muslim adherent like him (despite that he was only a convert to the faith).
[5] Tun Mohd Hamdan started his career in 1942 as a Native Clerk under the British North Borneo Chartered Company administration.
[7] Tun Mohd Hamdan Abdullah was well known as one of the founding fathers of United Sabah National Organisation which also known as USNO.
As Director of the Board, Tun Mohd Hamdan made important changes to help improve the agricultural irrigation and drainage system in order to increase paddy production.
Tun Fuad Stephens had formed a new political party known as BERJAYA to achieve his aims in order to topple the USNO Government.
The new administration was short-lived when Tun Fuad Stephens was killed in a tragic air crash which happened on 6 June 1976.
[15] Tun Mohd Hamdan died of heart failure at Istana Negeri, Kota Kinabalu on 10 October 1977.