The midfielder arrives on-loan from Chelsea to the end of the season.
"I am thrilled and honoured to be joining a great club like Borussia Dortmund," said Chukwuemeka. "I am looking forward to playing in front of the fans at Signal Iduna Park and contributing to the success of the team."
Borussia Dortmund has a long history of recruiting young English talent, with successful examples including Jadon Sancho and Jude Bellingham. England U21 winger Jamie Gittens is also making waves at the German club this season.
Dortmund sporting director Kehl said: "Carney is a very talented box-to-box midfielder who has already made his mark in the Premier League despite his young age. His dynamism, goal-scoring ability and determination, combined with great footballing class, make him a very interesting player.
"His development at Chelsea has stalled slightly, but we believe in his potential and are confident that he can find his best form here."