The 24-year-old goalkeeper has joined the Championship outfit on a season-long loan after it was clear that he was not part of Jose Mourinho's plans for the upcoming season.
Having spent six months with us a year ago on a loan spell from January onwards, it's always been known he was manager Steve Bruce's top target for between the sticks but it's been an incredibly long wait.
Johnstone has previously had loan spells with Scunthorpe United, Preston North End and Doncaster Rovers.
The Man United academy product made 22 appearances across all competitions for the Villians last term, conceding 26 goals and keeping eight clean sheets.
"I am delighted to be back", Johnstone told Villa's website.
"I just can't wait to get started again".
"I know he has given the club a massive lift and hopefully we can attract a couple bigger, players and regain our position back in the Premier League, where I think the club definitely belongs".
Johnstone, who has been handed the No.1 shirt, admitted the promise of regular first-team football was the key factor in his decision to return.