He had been appointed as mayor on 10 August and served in the position for just over a month.
A spokesperson confirmed to News24 that the mayor had died. This was further confirmed by two more sources in his office. A statement was expected to be issued on Saturday night.
Matongo had earlier on Saturday accompanied President Cyril Ramaphosa in Soweto, to campaign for the ANC ahead of this year’s municipal elections.
He had been elected unopposed as Joburg mayor, succeeding Geoff Makhubo, who died in July of Covid-19 complications.
Matongo served as the MMC for Finance under Makhubo.
He had risen through the ranks, from serving as a member of the Soweto Student Congress and the Congress of South African Students before moving on to serve as the regional head of communications in the ANC for eight years.
He had also served as the chief of staff responsible for the overall running and functioning of the offices of the Gauteng MEC for the sport and economic development and agriculture departments.
His mayoral candidacy provoked a heated contest between two factions in the ANC in the region.
Matongo and two other candidates became the first group to be interviewed by the ANC national top brass.
This happened under new rules that prospective metro mayors are interviewed by the ANC’s powerful top six, including Ramaphosa.