
Sky Sports reported that Union, third in the Bundesliga standings, paid a fee of up to £10 million (US$12.39 million) for the versatile 27-year-old.
Juranovic has 27 caps and played in six of their games at the World Cup in Qatar last month. He was on the bench when they finished third by beating Morocco 2-1 in a playoff.
Juranovic won the Scottish Premiership title and the League Cup in his first season with Celtic.
“The transfer to Union fulfils my dream of being able to play in one of the best football leagues in the world. The Bundesliga is intense and robust, which suits my game,” Juranovic said.
He will give Union more options in defence after Norway fullback Julian Ryerson’s move to Borussia Dortmund this month.