Napoli beat Arsenal and Chelsea to signing of Osimhen from Lille in £74m deal
The Serie A side fended off competition from Arsenal and Chelsea to sign the Nigeria international.
Osimhen was in demand after he scored 13 goals in 27 Ligue 1 appearances for Lille this season.
Napoli, who confirmed the signing on their official website, will finish in seventh place in Serie A, and will be involved in the Europa League next season.
Osimhen commenced his senior career at Wolfsburg and was sent out on loan to Charleroi, who then activated their option to sign him permanently prior to sanctioning a transfer to Lille last year.
The 21 year old has scored four goals in nine appearances for Nigeria.
Napoli forward Arkadiusz Milik has been linked with a move to Juventus, while there have been suggestions that Lille could replace Omishen with Rangers’ Alfredo Morelos, although such a deal has yet to materialise.