He is now in line to take over at Bloemfontein Celtic, where Clinton Larsen threw in the towel on Monday.
Maritzburg officials said they had not yet been officially told by Middendorp of his decision by the end of the work day yesterday afternoon, but had been inundated by calls from around the country after the news broke on social media yesterday afternoon.
A brief statement sent out by Middendorp's agent confirmed his departure. It read: "Ernst Middendorp has resigned from Maritzburg United Football Club."
His agent, Steven Kapeluschnik, confirmed that after spending altogether nearly three-and-a-half years at the club and being in charge of the team for approximately 100 games, he has decided that it is time for him to move on and look for new challenges in his career.