The right-back -who was initially targeted by Newcastle in the summer after impressing at Euro 2012 - has joined the struggling club for an undisclosed fee, signing a five-and-a-half year deal.
Debuchy, 27, has been capped 12 times for France and made in excess of 230 appearances for the 2011 Ligue 1 champions after coming through Lille's youth set-up.
"It is great to become a Newcastle United player," Debuchy said. "After many great years at Lille I felt I was ready for a new challenge, and cannot wait to play for such a big club in the best league in the world.
"I hope I can bring something fresh to the team and help us get up to the highest possible position in the Premier League this season. I will give everything for this club."
Manager Alan Pardew added: "We are absolutely delighted to have finally secured the signature of Mathieu. It's no secret we've been trailing him for some time now and to have reached this point fills me with great excitement and anticipation in respect of what he will be able to offer the team.
"At the same time it's a huge relief to actually have him with us now. He is an established top international player and it is a real coup for this club that we now have him at St. James' Park.
"Mathieu will add real quality to our team, in terms of his ability, character and experience and I am sure he will quickly become a firm favourite among our fans too."
- Sports & Recreation