Sibusiso Mashinini was born to Johannes and Catherine. Unlike his brothers and sisters, he was very quiet and more helpful at home. He was remarkably intelligent, which was noticeable at an early age. According to his father, when Mashinini was three, a dentist commented that his set of teeth told of his remarkable brilliance. At the age of about 11, he helped his father find an ageing uncle in the deep rural of the Orange Free State. As a result of Mahinini's persistence in investigating, through investigative letter writing, he located the uncle and communication resumed. It resulted in his uncle moving closer to the Vaal Triangle. This is a particular deed that his father's asserts will stay with him. As a young boy Minus would rush home from school to carry out his duties and then tell his parents he was attending a rehearsal in the neighbourhood. The supposed rehearsal was in fact where he would meet other young activists where they would discuss politics and plan political actions.
He left the country at the age of 15 but he had a more or less two year service in underground cells of the African National Congress (ANC). He left the country during the month of August 1976. It was only after Mashinini left for exile, that his parents got to know about his hidden political activities.
When the June 16 uprising started, Mashinini was 15 years old. He was a student at Orlando West Junior Secondary School. His politicisation was done there. He served on the Soweto Student Representative Council (SSRC), which meant that he served as a representative for his school to an umbrella student body. The SSRC planned and staged the 1976 students uprising in Soweto. His leadership skills were shaped by that participation in politics. After the uprisings, he, like thousands of other students were forced to leave the country to go into exile. He joined the ANC in Swaziland and belonged to the Umkhonto weSizwe (MK) detachment. While in exile his nom de guerrre became "Minus Khosing". He received his military training in Russia, Chekoslovakia and China. He was advanced to the ordinance unit of the MK and thus instrumental in the smuggling of arms for military operations in South Africa.
Mashinini was also a member of the Communist Party.
In exile he married Elizabeth Makamu, a Mozambican. Mashinini died in exile in Zambia, October 1990 under mysterious circumstances. The heading of a local newspaper read: "HIGH PROMISING CADRE DIED IN EXILE". The report partly read that his private parts were missing and eyes gorged, which was indeed mysterious.