The 29-year-old has signed for L'OM on a three-and-a-half year deal but for now will be focusing his efforts on the national team as they get ready for the Africa Cup of Nations
The former Cannes and Amiens creator only had six months remaining on his contract, enabling Ligue 1's third-placed team to secure the player for a nominal fee.
Kadir will provide competition for the likes of Mathieu Valbuena and Andre Ayew when he returns from international duty with Algeria.
"Selected with Algeria for the 2013 Cup of Nations in South Africa, the new recruit will temporarily leave Marseille in January, but he participated in his first practice session on Wednesday," the club announced on their official website.
Kadir enjoyed a productive first half of the season, scoring six goals and making seven assists for Valenciennes.