The highly-rated 22-year-old has been linked with a move to the Premier League for several years now, and Alan Pardew's side has won the race for his signature, according to the Ligue 1 club's official Twitter account.
The message read: "Moussa Sissoko is leaving his hometown club, Toulouse FC, to join Newcastle!"
The two teams are believed to have agreed a reduced fee of 1.8 million pounds, as the player's contract was set to expire at the end of the season.
The box-to-box midfielder has allegedly signed a five-and-a-half year contract, and will complete the move after undergoing a medical.
The Magpies are currently 16th in the Premier League after a disappointing first half of the campaign, following their fifth-placed finish last season.
But Pardew has moved quickly in the January transfer window in a bid to arrest their slump, though Demba Ba left the club for Chelsea at the start of the month and club captain Fabricio Coloccini's future is in doubt.
Sissoko is the fifth Frenchman to join Alan Pardew's side in the January transfer window, following Mathieu Debuchy, Mapou Yanga-Mbiwa, Massadio Haidara and Yoan Gouffran from Ligue 1 to St. James' Park, and you can find out more about those players here.