Paul Ramotsoane Mosaka was born in Johannesburg and received his early primary education there. His secondary education was at Headltown near Fort Beaufort in the eastern Cape. He read for a Bachelor of Arts degree with the University of Fort Hare. While still studying, Mosaka became involved with the Transvaal Student Association. After completing his studies he began his career as a teacher at Healdtown before moving to Thaba Nchu in the Free State. After a while in Thaba Nchu he returned to Johannesburg and managed one of James Moroka's businesses. He married Miriam Ncamziwe Mosaka in 1940 and fathered four children.
In 1992 Mosaka was elected to the Native Representative Council (NRC), which emanated from the Hertzog Native policies. He caused a stir by calling the NRC a toy telephone. His national prominence grew after he was appointed to the Atlantic Charter Committee by the African National Congress to study problems and issues concerning African rights contained within the Atlantic Charter. The United Kingdom and United States of America drew up the Atlantic Charter as a post war peace and security charter. The Atlantic Charter Committee drew a response from the standpoint of Africans and called it the African Claims.
During the Alexandra Bus Boycott, Mosaka was a member of the Emergency Transport Committee, which gave assistance to bus boycotters. He was arrested and later released from prison. On 26 September, 1943 Mosaka, in conjunction with senator Hyman Basner, formed his own political organisation, the African Democratic Party. His intention was that the organisation should remain an ANC affiliate. Due to A B Xuma's strict African nationalist view, the ADP was forced to be on its own.
He continued with his political activism by taking part in the 1944-45 rallies of the Campaign for Right and Justice. In 1945 he was involved with the communist Party of South Africa's Anti-Pass Campaign. The ADP allied with James Sofasonake Mpanza to organise the invasion of empty land to protest against lack of housing and slum conditions caused by overcrowding in Orlando, the first township of Soweto. By October 1946, the ADP was facing its demise. In the meantime, his businesses were flourishing and by the 1950s he was focusing most of his energies in running them. In 1955, he became president of the Johannesburg Black Chamber of Commerce. This year was also a year of crisis in Black education. The government was planning to implement its 1953 Bantu Education Act. Mosaka controversially critiqued the ANC's education boycott against the introduction of Bantu Education. The following year, he took part in a conference organised by Interdenominational African Ministers to discuss the infamous Tomlinson Report on the Socio-Economic Development of Bantu Areas. The report was harshly criticised and rejected by the conference. He also took part in an ANC organised conference to discuss the political circumstances of Africans in the face of political bannings and the formation of the Republic of South Africa. He was elected to the important continuation committee of the ‘All in' conference, which decided to call for a national conference of all African leaders. However, due to ill health, he was unable to attend any of the meetings and resigned in 1961. He was still arrested for his involvement in the conference. On his release from prison, Mosaka dedicated his last years of life doing business. He died while on a business trip to Swaziland.