Born in 1914 Mahlangu was a trade unionist. As a domestic worker Mahlangu took part in the 1942 anti-pass campaign and was sacked. Later he was again victimised after taking part in a strike at a power station. He became a full-time trade union secretary after entering the laundry industry.

He was an Executive Committee Member of the South African Congress of Trade Unions from 1955-1956.