Nkoudou, 21, has spent the last few weeks in London waiting for his move to White Hart Lane to be finalised but complications in talks between the two clubs delayed the move.
The France Under-21 international dropped a hint on Tuesday evening suggesting the deal was finally done, tweeting an image featuring Tottenham's club motto 'to dare is to do."
Spurs have now confirmed the move with Nkoudou signing a five-year contract with the north London side. He will wear the no. 14 shirt at Tottenham and told the club's website: "I can't wait to get to know the Premier League and the English game. It suits my playing style, it is explosive. Everyone knows I am fast, I like to dribble around players so the English league is best for me. I am exciting and can't wait to get started."
Nkoudou cost Marseille just £1m from Nantes last summer, scoring five goals in 28 Ligue 1 appearances last term. He becomes Tottenham's third signing of the summer following the arrivals of Netherlands international Vincent Janssen and former Southampton midfielder Victor Wanyama.
Tottenham also remain heavily linked with a deadline day move for Newcastle United midfielder Moussa Sissoko, while the club are also still hoping to seal a move for Espanyol goalkeeper Pau Lopez.
The Spanish side have already suggested they have a replacement for 22-year-old Lopez lined up with an verbal agreement already reached between the two clubs.
The Evening Standard now claim Spurs still expect so seal what will be an initial love move for the Spaniard, despite there being just over three hours of the summer transfer window remaining.