Djemba-Djemba, who was nicknamed "little Cantona" by friends during his childhood in Cameroon, passed a medical on Wednesday afternoon and has agreed a deal with the Buddies until the end of the season.
The 32-year-old has been assigned the No.99 shirt and St Mirren boss Danny Lennon said: "He is a top-drawer player who does a power of work in the defensive midfield area.
Eric Djemba-Djemba looks forward to a career north of the border
"He wants regular football to ensure he goes to the World Cup with Cameroon this summer and we are happy to give him that platform."
Djemba-Djemba signed for United from Nantes for £3.5 million in 2003 and went on to make 39 appearances for the club.
He scored two goals - including an extra-time winner at Leeds in the League Cup - and claimed an FA Cup winners' medal before he was sold to Aston Villa on January transfer deadline day in 2005.
The Cameroonian has since notched up spells at Qatar SC, Danish side Odense, Hapoel Tel Aviv in Israel before moving to Partizan Belgrade last summer.