The Blues activated Werner’s €60m release clause last month, meaning all that had to be agreed upon was personal details to secure the player's move to Stamford Bridge.
Werner told Sky Sports: “The discussions with the board at Chelsea were so good that I ultimately chose them.
"Frank Lampard in particular stood behind me and really wanted me to know that if I went to Chelsea, I could feel just as comfortable as I do with Leipzig.
“In the conversations with me, the coach often emphasised how much he wanted me, how much he valued me as a person. Of course it's hard to give up an oasis of wellbeing like the one I've had in Leipzig for years, but you can only get ahead in a career if you take the next step.
“This season was the crossroads, otherwise I would always have stayed with Leipzig. I’ve decided on something new and I hope that my form will continue like this.”
Werner leaves RB Leipzig with fond memories, and reserved praise for Julian Nagelsmann, who has been key in developing him into one of the most potent strikers in Europe.
“I’ve been received in Leipzig like never before in my career,” he said of his time with the club.
“No matter which coach was in charge, I always had supporters here. Now there is Julian, who is again a giant and is someone who has made me significantly better.”