Grealish’s departure had been anticipated since the Premier League champions submitted a mammoth offer late last week and an agreement between the clubs is now thought to be close.
Barring any late hitches, the 25-year-old is expected to undergo a medical and it is possible the deal could be completed by the end of the week.
Grealish will become the most expensive British player of all-time with the deal eclipsing the £85m Real Madrid paid to take Gareth Bale from Tottenham in 2013.
It will also exceed the existing Premier League record fee, which saw Paul Pogba join Manchester United from Juventus for £89m five years ago.
Villa had been hoping to convince Grealish to stay and were ready to offer him a new contract on considerably improved terms.
But it is thought Grealish was eager to test himself in the Champions League and the chance to join City is one which has ultimately proved too good to turn down.
Villa, who confirmed the signing of winger Leon Bailey from Bayer Leverkusen for an initial £25m early on Wednesday morning, will reinvest the money received for Grealish as they look to maintain their own lofty ambitions.
A move for Chelsea striker Tammy Abraham is expected while Burnley’s Dwight McNeil is also on the club’s radar.