Yanga-Mbiwa was born in Bangui, Central African Republic but moved to France as a toddler growing up in the commune of Port-de-Bouc, not far from the city of Marseille, in the department of Bouches-du-Rhône. He joined Montpellier as a youth player in 2005 and made his professional football debut on 23 February 2007 in a 0–1 defeat to Bastia starting the match and playing the entire 90 minutes, picking up a yellow card. Following the season, he signed his first professional contract agreeing to a three-year deal until 2010. He was officially promoted to the senior squad and was assigned the number 3 shirt.

Initially, Yanga-Mbiwa was utitlized as a substitute earlier on during the 2007–08 season, but by September 2007, despite being only 18 years old, Montpellier manager Rolland Courbis named Yanga-Mbiwa a starter for the rest of the 2007–08 season. Yanga-Mbiwa didn't disappoint appearing in 41 total matches scoring one goal. Beginning with the club's 31 August 1–0 victory over Ajaccio, Mbiwa appeared in every match Montpellier played including the Coupe de la Ligue and Coupe de France matches, where Montpellier reached the Round of 16 and Round of 32, respectively. His only goal of the season came on 12 May 2008 against FC Gueugnon scoring the winner in injury time to give Montpellier a 2–1 victory.

Already established as a regular, Yanga-Mbiwa was an incumbent starter heading into the 2008–09 season, and despite competition from fellow youngsters Mickaël Nelson and Abdel El Kaoutari, he continually impressed appearing in 33 total matches and scoring one goal against Angers in a 3–3 draw again in injury time. The equalizing goal came only seconds after Angers took the lead with a goal from Malik Couturier. On 20 March 2009, with Montpellier in a decisive battle for promotion, Yanga-Mbiwa picked up an extensive injury against Brest, which ruled him out for almost two months. He returned to the team on 8 May 2009 and played the final four matches helping Montpellier achieve promotion to Ligue 1 on the final day of the season.

Despite promotion to Ligue 1, with his impending stint in prison oncoming, manager Rolland Courbis resigned from his position and new manager René Girard came on. Girard made it clear that one of his many priorities were to keep hold of Yanga-Mbiwa and on 2 June 2009, it was done with the club signing the player to a two-year contract extension until 2012. Yanga-Mbiwa made his Ligue 1 debut in the club's opening match of the season against Paris Saint-Germain playing the entire match in a 1–1 draw. On 12 May 2010, Yanga-Mbiwa added an extra year to his contract after agreeing to a contract extension with the club.