City won a thrilling encounter 4-3 at Eastlands on Saturday but Hughes gave what appeared to be a farewell wave to the home fans at full-time amid talk that a boardroom fall-out had led to his resignation earlier in the day.
Hughes had been in the City hot-seat since June 2008 but his future had been brought into doubt following a mixed series of results this season.
He spent heavily during the summer to bring players of the calibre of Emmanuel Adebayor, Kolo Toure, Gareth Barry and Roque Santa Cruz to the club, but was rumoured to be under pressure at the beginning of the month following a run of eight successive league draws.
His situation appeared to worsen earlier this week after a claim from Guus Hiddink's agent had been contacted about the potential availability of the former Chelsea manager.
Former Internazionale coach Roberto Mancini, who was also strongly linked with any managerial vacancy in reports in Saturday's newspapers, will replace Hughes.
They claimed that City's ambitious Abu Dhabi-based board was beginning to lose patience with Hughes following their heavy investment in the club during their 18 months in charge.
Hughes, whose first club managerial job was with Blackburn Rovers, won just 36 of his 77 games in charge of the Citizens after replacing Sven-Goran Eriksson in the managerial hot-seat.
The 46-year-old former Manchester United star cut his managerial teeth with a successful spell in charge of his native Wales.