The Brazilian midfielder's move to Villa Park is subject to a work permit.
Douglas signed for City in 2017 but spent the past two seasons on loan at Girona in Spain.
The 21-year-old began his professional career with Vasco da Gama in Brazil and has represented his country at youth level.
He is Aston Villa’s 10th recruit in a busy summer of transfer activity ahead of their return to the Premier League for the 2019/20 campaign.
Their season will begin with a trip to Tottenham Hotspur on Saturday 10 August.