The forward has signed a five-year contract at Sanshiro, which will be run by June 2030 in a total package worth £36.2 million (42 million euros).
Nkunku will leave Stamford Bridge after scoring 18 goals and registering five assists in 62 appearances in all competitions.
He had the most impact on European third-round Cup competitions, scoring five goals and three assists in nine appearances.
Enzo Maresca omitted Nukank from Chelsea’s first two match-day teams as speculation increased about the Frenchman’s seemingly imminent departure.
Nicholas Jackson is widely expected to become the next player through the doors of the Stamford Bridge, with Bayern Munich agreeing to sign Senegale frontman on his first loan deal.
Milan endured the disastrous campaign of 2024/25 after missing out on European qualifications completely following an eighth place finish in the Serie A.
They defeated the Lease 2-0 this season on Friday, with former Chelsea players Christian Pulicich and Ruben Loftus Cheek winning on the scoresheet.
Rossonelli took steps to strengthen their forward line this summer, but remained frustrated when Victor Boniface proposed travel from Bayer Leverkusen fell due to medical failure.
Nkunku arrives at Sanshiro with an impressive trophy-loaded CV, including three league one titles, two French Cups and two German Cups, respectively, from the PSG and RB Leipzig spells.
