Mbenza's previous contract was due to finish at the end of last season, but Town triggered a 12-month option in his deal to prevent him leaving for free.
It was a move largely designed to protect Town's interests.
But while Juninho Bacuna - who also had a 12-month clause in his contract activated - left the club in the summer window, joining Glasgow Rangers after a deal was struck, Mbenza remained at the club by the closure on business on Tuesday night.
A deal has now been struck with Town to enable him to leave after both parties agreed a settlement.
The player has subsequently joined Qatar Stars League outfit Qatar Sports Club.
Mbenza joined Town from French Ligue 1 side Montpellier, initially on loan, in August 2018.
Previously, he had played for another Valenciennes, and Belgian side Standard Liège.
He made 41 starts and 26 substitute appearances during his time at the club, scoring six times.