The France international has signed a six-year contract with a side that finished 12th in the Premier League last season, missing out on European football entirely for next season.
Nkunku agreed to join Chelsea last year before the Blues endured one of their worst seasons in recent memory.
Nonetheless, Nkunku is not perturbed about swapping RB Leipzig for Chelsea as he aims to improve as a player and help restore his new side's place among the best in Europe.
“We can say that I am a hard worker,” Nkunku told the club’s website, chelseafc.com.
“I will give everything for the club, for the fans and to help the team bring some trophies, to give the best of my football.
“I hope I will make them as happy as I am to be here at this club.”
“I think the project was good for me. It is a good project for me to develop myself as a player and a man also.
“And this is a good city, after all, and for sure I want to improve in football and I want to win trophies and improve myself also.”
The 26-year-old scored 23 goals in 36 games for Leipzig last season as they finished third in the Bundesliga and won the DFB-Pokal for the second successive season.
Nkunku started his career at Paris Saint Germain, where he won three Ligue 1 titles before joining Leipzig in the summer of 2019.
He has won ten caps for the France national team but missed the Qatar 2022 World Cup through injury.
