The France international, who is currently representing his country at Euro 2012, has completed a transfer to the Grand Stade Lille Metropole for a reported fee of €10 million
The 24-year-old midfielder has signed a five-year contract with the 2011 French champions after the two clubs agreed on a reported €10 million deal.
Sochaux president Alexandre Lacombe had revealed earlier in the month that an agreement had been reached between the clubs, but only now have Lille officially unveiled the player.
"I am very happy," Martin told Lille's official website. "I wanted to sign for Lille because they are an ambitious club I have been interested in for a long time.
"You can talk about a real choice here, and I hope from all my heart that everything will go well."
Martin, who has 14 France caps to his name, has made two appearances for Les Bleus at Euro 2012, both as a substitute.