The 22-year-old, who is on a five-year contract at White Hart Lane until 2020, said: "I'm ready to give my best to help the club achieve its aims."
N'Jie scored seven goals for the Ligue 1 side last season and has netted six in 10 appearances for Cameroon.
His arrival follows the departure of Spain striker Roberto Soldado to Villarreal.
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Tottenham have signed Cameroon international striker Clinton N'Jie from French club Lyon.