Nimrod Boyce Tantsi was born in Johannesburg in 1895, the grandson of one of the founders of the AME in South Africa. His family moved a number of times during his youth, first to Natal and then to the Cape, where Tantsi completed his education to the Junior Certificate level at Cota High School in Idutywa, an AME school founded by the Maxekes. After working for some time as an insurance agent in East London, he taught briefly in Bloemfontein, then in 1924 returned to Johannesburg where he began to study privately for the ministry. At this time he also helped Clements Kadalie in his initial efforts to establish the Industrial and Commercial Workers' Union in Johannesburg. Already a member of the ANC, Tantsi was posted to Witbank as a full-time ANC organiser for the eastern Transvaal. When the short-lived League of African Rights was set up by the Communist Party (CPSA) in 1929, Tantsi became one of its leaders. At this time, together with Edward Roux, he composed the popular political song "Mayibuye." A member of the Transvaal ANC executive committee from the late 1920s, Tantsi became official Transvaal chaplain in about 1938. At the time of the 1952 Defiance Campaign, when Nelson Mandela was fully occupied with the conduct of the campaign, Tantsi became acting Transvaal president.
In 1953 he was issued banning orders forbidding him to attend meetings. At that time he was a presiding elder of the AME and was resident in Lady Selborne township, Pretoria. He was also active in the Interdenominational African Ministers' Federation. In April 1959 he attended the inaugural conference of the Pan Africanist Congress (PAC). Following the Sharpeville massacre he was involved in the efforts to regroup African forces through the "all-in" conferences of December 1960 and March 1961, an involvement which led to his arrest, at the age of 66, together with other members of the continuation committee, following the second conference. Their conviction was reversed on appeal. He is the author of a Historical Sketch of the AME Church in South Africa (1940).