The 24-year-old forward has signed a five-year contract with the Blues worth just over £170,000-a-week and will move to England at the end of the Bundelsiga season.
“I am delighted to be signing for Chelsea, it is a very proud moment for me to be joining this great club,” said Werner. “I’m now going to the amazing city of London. It was clear to me that I would take this next step abroad – that was always my dream.
“So it’s not a decision taken against Leipzig, just one to complete my dream of playing in the Premier League – the strongest league in the world. I now have the chance to play for one of Europe’s top clubs. I’m looking forward to this adventure, the atmosphere and English football.
