The former Bordeaux attacker described the switch as "a great move" despite leaving the current Barclays Premier League champions.
He told his new club's website, nufc.co.uk: "I spoke with some of my friends and Newcastle is a big club with history in England, so it's a great move.
"I'm just really happy to be here because this is still a big club for me.
"It wasn't really a difficult decision to come here.
"I spent two good years in Manchester but it was a bit difficult with the competition and I really needed a club where I could play more games.
"I know it won't be easy to play each game here, because there's a good group, but I want a fresh start in my football."
He added: "I've heard a lot about the fans, the atmosphere, the passion around the club and the way the city is just behind the club 100%.
"So I think I'm going to love it."