"After inheriting R2bn operating deficit municipality, the DA-led government tried its best to serve the people of this capital city," wrote Msimanga.
"The list of the work we have done is endless, however the true test of our term is the impact we have made to the lives of our VIPs, the residents of Tshwane."
Msimanga urged residents of Gauteng to rally behind him in the race for the province's premiership ahead of the upcoming general elections, saying his Tshwane track record proved that he can run "a clean government".
The ANC caucus chief whip Aaron Maluleka said Msimanga's resignation did not follow the proper process as he first announced it to the media two weeks ago.
"The executive mayor cannot resign in a press conference. He disrespected council," said Maluleka.
"The mayor must follow process in a form of a report. If Msimanga did not know about that, we will teach him," said Maluleke.