The Dutch Under-21 international joins FC Nordsjaelland defender Jores Okore and Bulgarian winger Aleksander Tonev in signing for the Villa Park outfit.
Bacuna made 33 league appearances for Eredivisie side Groningen last season, scoring five times, and is delighted to have made the switch to the Premier League.
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"This is a dream come true for me and also for my parents who are delighted for me. It's a tremendous league to be a part of, the Premier League, and we want to show that Aston Villa can takes its place among the top teams.
"I'm really excited to come here. Villa Park looks magnificent and the training facilities at Bodymoor Heath are first class. I'm really impressed with the set-up here and I'm proud to be a part of this club.
"The manager is trying to create a new generation, to build something here and make a lot of young guys show what they can do. I'm up for the challenge."
Villa boss Paul Lambert has described the 21-year-old as a “real asset” and believes he can have a big impact next season.
"Leandro's energy and versatility will be really good for us," said the Scottish manager.
"He's a good player, he has bags of energy and he will make an impact. He's another player we believe will do well for us. He has played in big games and he has lots of experience for a player so young."