The film will be based on the Lynott biography MY BOY by his mother PHILOMENA.
Mumba will play the young Lynott, while Dourdan will play the rocker in his Thin Lizzy days.
The movie will be shot later this year in and around Dublin, Ireland and is expected to be released in 2007.
Lynott died in 1986 after a multi-organ failure brought on by years of drug abuse. He was 36.