The Championship side have recruited the Saint Lucian on a season-long loan deal that will become permanent once his work permit application is cleared.
Donacian, who can play anywhere across the defence, scored once in 80 league appearances for Stanley since his 2016 switch from Aston Villa.
"Janoi is a great lad, he is a model professional," Accrington chairman Andy Holt told the official club website.
"He came here, grafted, helped us win the league title and fully deserves his opportunity. That's what we are about at Accrington.
"The fee means a great deal to us and for us, it's going into new changing rooms."
Donacien played in all but one of Accrington's league matches last season as they won the League Two title.