After 183 appearances for Wolfsburg, Knoche has moved to the German capital with Union.
Knoche said: “When you’ve played for a club for fifteen years, a change is probably not easy for any player.
“Nevertheless, I’m happy to be playing for 1. FC Union Berlin now. The club has developed very well and many fans have been surprised and enthusiastic about it over the past year.
“The discussions with the people in charge were extremely positive, and that was the decisive factor in my decision to join Union.”
The club’s director of football Oliver Ruhnert said Knoche will bring added flexibility to the Union side.
“With Robin Knoche, we have been able to sign a very good central defender who has enormous experience in the Bundesliga,” said Ruhnert.” With his excellent positional play, his height and his strong build-up play, Robin will not only strengthen our defence, but also make us more flexible in terms of our play.”
Union finished 11th in the Bundesliga this season after winning promotion through the play-offs.