Clinton N'Jie was convinced to go on loan in the opposite direction and the Spurs forward has now completed his temporary move to France.
Spurs have long since agreed a £9.9m fee for the France U21 international, who made 40 appearances in two seasons with Nantes before joining Marseille in June 2015.
N'Koudou impressed with OM, scoring 10 times in 41 appearances and struck four goals in the Europa League.
He had agreed personal terms with Spurs last month and has been training at Hotspur Way as the two clubs finalised the transfer. The deal was delayed by a change of presidency at Marseille.