Borussia Dortmund have extended the contract of defender Erik Durm until 2019.
The 26-year-old signs from Houston Dynamo, who he helped to two consecutive Major League Soccer Cup finals.
Manager Derek Adams told the club's official website: "Our interest in Andre has been no secret and when you look at his record that's no surprise.
"Despite still only being a young player, he's got experience of playing in Europe as well as at a top side in the MLS which is now an extremely good league which features world class players.
"Signing players from outside the EU does involve a lot more work in the background to secure the necessary clearance and visas, but this work has now secured us a player who will undoubtedly add to the squad here at Ross County."
Hainault joins Ivan Sproule, Evangelos Ikonomou and Steffen Wohlfarth in signing for the Dingwall side this month.