The striker is returning to his homeland, subject to international clearance being granted, after the two clubs agreed on an undisclosed fee.
QPR manager Ian Holloway told the club's official website: "I am sorry to lose Seb. He is a great professional and has an attitude that I love.
"Whether it's in training or in matches, he gives you everything he's got. His desire and commitment made him very popular with the fans here, which tells you everything.
"We wish him every success in the future because he is a man who deserves it."
Polter joined QPR from Mainz 05 in the summer of 2015, scoring 11 goals in 56 appearances for the Championship club.