Chelsea on Thursday confirmed they have reached an agreement to sign the prolific forward, subject to a medical.
The Premier League club will reportedly pay £47.5million (€53m) for the 24-year-old, with the length of his contract not disclosed but said to run until 2025.
Werner, who will arrive at Chelsea in July after the Bundesliga season ends, was linked with a host of the biggest clubs in Europe – including the likes of Liverpool, Manchester United and Bayern Munch.
However, the Germany international is confident a switch to Stamford Bridge was the best option.
He tweeted along with a video: "I'm incredibly happy to be joining the Blues next season! It feels like the right step for me and I am delighted to become a part of Chelsea FC.
"Really looking forward to playing for such a fantastic and historic club! See you soon Chelsea fans!"
Werner, who has scored 32 goals and set up 13 in all competitions this season, also posted a message to Leipzig fans explaining his decision to depart.
He wrote on Instagram: "After 4 wonderful and formative years it is time to tell you that I have decided to move to England next season.
"I take this new step in my life with great anticipation but with a heavy heart. I can still remember well when I came to Leipzig in 2016 when I was 20.
"My first game against Hoffenheim, my first home game against Dortmund, my first goal against HSV ... Well, 4 years later, I can look back on so many wonderful experiences, successes and encounters that I will always keep with me.
"So I want to say THANK YOU. THANKS to the fans, my team-mates, those responsible, the employees, to all the other people I've met here so far and to this wonderful city of Leipzig, where I felt at home from day one.
"At the same time, I am really looking forward to this new, exciting chapter in my career in England, which starts for the new season.
"Now, of course, the first thing is to successfully end the season in Leipzig!"