The 23-year-old France international has put pen to paper after passing a medical on Tyneside and agreeing personal terms.
Yanga-Mbiwa, who will reportedly cost Newcastle around £7million, is backing Newcastle to improve their current league position this season and then eventually challenge for honours.
"I don't think it (the league position) is a concern at the moment," he said. Newcastle is a massive club and while we are not in an ideal position at the moment, I think we can definitely finish in the top half of the table.
"In the long term people talk about the top four in the Premier League and I think with the players we have got on board and the manager and his ideas, we can definitely close the gap, get in the top six and, in the long term, why not challenge for the title?"
Newcastle manager Alan Pardew added: "We needed to strengthen the team and bringing in Mapou will give the whole squad a boost. He is precisely the sort of player we've been looking to bring to the club.
"He is a good age for us but has plenty of experience at club and international level. Mapou is a talented footballer, good in the air and on the ground and has all the attributes to succeed as a quality defender in the Premier League. He's a good character too and that will be important for us over the next few months."