Budenholzer will sign a four-year contract, according to ESPN's Adrian Wojnarowski.
"His leadership, basketball intellect, championship-level experience and communication skills make him the right fit to take our team to the next level," Bucks GM Jon Horst said.
Budenholzer coached the Hawks for five seasons, racking up a 213-197 record. He was largely credited with Atlanta's East-best 60-22 record in 2014-15, taking a mostly veteran team to the conference finals.
A Gregg Popovich disciple, Budenholzer was an assistant with the San Antonio Spurs from 1996-2013.
Following three underachieving seasons under Jason Kidd, the Bucks represent a coveted opportunity, with Antetokounmpo under contract until 2021.