He was born in 1924 near Mafeteng, Basutoland (now Lesotho), the son of an Anglican minister. In 1940, while a student at Lovedale, he concealed his age and enlisted in a non-European transport unit of the South African Army. After the war, he returned to his studies and became an organiser for the African National Congress Youth League in Lovedale.
Following a student strike he was expelled but completed his training course at Wilberforce Institute and took up teaching in the Transvaal. Strongly influenced by the nationalist views of Anton Lembede and A. P. Mda, Leballo continued to be active in Youth League affairs, and after the 1952 Defiance Campaign his home in Orlando Township became a gathering place for partisans of the Africanist faction.
By 1954, Leballo had seized leadership of the Youth League in me Orlando East Branch, and the Africanist began to appear regularly, carrying his strongly worded attacks on the African National Congress's (ANC) leadership. Throughout a series of expulsions and reinstatements by the ANC, he retained his hold in Orlando and carried many of the branch members with him into the Pan Africanist Congress (PAC) in 1959. Deferring with his followers to the more intellectual and prestigious Robert Sobukwe at the time of the PAC's founding, Leballo became PAC national secretary. His zeal and flamboyance as an organiser did much to attract a following for the PAC, especially among the young, but his speeches and actions also contributed to the prevailing view among the whites that PAC was a racist movement bent on violence.
Following the 1960 Sharpeville emergency, Leballo was sentenced to two years in prison, and on his release was banished by the government to the Native Reserve No.14, Ubombo District, Natal [now KwaZulu-Natal] on 25 March 1960.
His banishment order stated that he was the National Secretary of the Pan Africanist Congress (PAC) and a member of the Basutoland African Congress. Additionally, he was well known to the police for his political activities in leftist campaigns against the state since 1952. Leballo appeared in court and was found guilty of incitement and jailed.
A new banishment order was prepared, to be served upon his release from prison on 3 May 1962. This again banished him to the Ubombo district. Leballo escaped from banishment and fled to Basutoland and then to London.
His banishment order was revoked on 7 September 1962. Leballo went back “to Basutoland [Lesotho] where he was born. Here the Basutoland authorities accepted him.
Using the argument of his birth in Basutoland, he successfully appealed for permission to leave South Africa. In August 1962 he went to Maseru, where he and other released leaders began efforts to reconstruct the PAC.
He subsequently made a trip to New York to petition for United Nations action against South Africa. In March 1963, a reckless move in Maseru exposed him to a storm of criticism from other PAC members and weakened the lines of authority that remained in the organisation. Calling a press conference, he announced that Poqo terrorist attacks were linked with PAC plans for a nationÂwide uprising. Within a week Basutoland police raided PAC offices, and captured a lengthy list of members, many of whom were then arrested in South Africa. Leballo escaped before the raid, hid out for some months, then left Lesotho and established PAC headquarters in Dar-es-Salaam.
He is now recognised by the Organization of African Unity as acting head of the PAC, although his claims to leadership have repeatedly been challenged by other former officials of the organisation. In 1970 he appeared as the key state witness in the trial of seven Tanzanians convicted of plotting to overthrow President Julius Nyerere.