Horst will take over a young, promising roster led by All-Star forward Giannis Antetokounmpo. The Bucks finished above. 500 for the first time since 2009-10, losing to the Toronto Raptors in the first round in six games.
The franchise is also moving into a new downtown arena next year.
Horst was hired by the Bucks as basketball operations director in 2008.