Before joining the Communist Party of South Africa (CPSA) in the 1920s, Thibedi was a member of the International Socialist League in the Cape and, according to Roux, for some years the only African Communist in South Africa. An able and dedicated organiser, he served, at its establishment in 1925, as the supervisor of the party night school in Ferreirastown, Johannesburg. The same year he was elected to the party's central executive committee. With Benjamin Weinbren he worked in the mid-1920s to establish African workers' Organisations, personally acting as the secretary of most of the fledgling unions established, as well as being the chief organiser and later the general secretary of their co-ordinating body, the Federation of Non-European Trade Unions. In 1929 he was a member of the executive committee of the short-lived League of African Rights.
Deeply involved in the factionalism of the Communist Party in the years following 1929, Thibedi ”” who supported S. P. Bunting and opposed the "Native Republic" slogan ”” was expelled from the party in 1930 on the grounds that he had mismanaged union funds. Following his expulsion, he worked with Bunting in an effort to launch an African mineworkers' union, a task to which the South African left would return with greater success a decade later. In 1932 he made an abortive attempt to found a vernacular newspaper called Maraphanga but it folded after one issue.