[3] The family moved to London when Shamash's brother-in-law Robert Sheldon was elected to Parliament in 1964.

[4] Shamash joined the Labour Party in 1969 after involvement in student politics and the Anti-Apartheid Movement.

[3] Shamash attended North Cestrian Grammar School and Burnage Grammar School in Greater Manchester, and studied human and physical sciences at the University of Surrey to become a dentist before training to become a solicitor.

[4] One of the first firms to be granted a Legal Aid Agency contract,[5] it merged with Edwards Duthie in 2019 to form Edwards Duthie Shamash,[2] and Shamash heads its parliamentary, electoral and media law practice.

[4] In the 1979 general election, Shamash stood unsuccessfully as a Labour Party candidate in the safe Conservative seat of Shoreham.