The 23-year-old centre-back put pen to paper on Tuesday, with the Premier League club choosing not to disclose the transfer fee they paid to the French outfit.
"It is an honour to be able to come to Newcastle United and have the chance to play in the Premier League," Yanga-Mbiwa told the club's official website.
"Newcastle are one of the biggest clubs in the league, and I'm going to try and give everything I have so that the team can do well.
"I have experienced a lot of positive things so far in my career and one of those is joining this club."
Newcastle manager Alan Pardew believes that Yanga-Mbiwa's addition to his squad will give them "a boost" for the second half of the season.
"We needed to strengthen the team and bringing in Mapou will give the whole squad a boost," he said.
"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."
Yanga-Mbiwa made over 200 competitive appearances for Montpellier.