First Team squad member Lubala made four appearances for Blues last season, three off the benchbcfc.com
Blues have an undisclosed sell-on clause as part of the deal that has taken the forward to the League Two outfit.
Lubala's existing contract was due to expire at the end of this month.
The 21-year-old links up with former Blues coach Gabriele Cioffi, who is in charge at Crawley.
Born in the Democratic Republic of Congo, but growing up in Leicester, Lubala joined the Blues Academy in 2016.
He became a regular for Blues Under-23s before making his First Team bow as a second-half substitute in a Championship fixture against Bristol City in April 2018.
Last season saw him rack up six appearances for Blues Under-23s, and four for the First Team - three of which came off the bench.
Birmingham City thanks Bez for his contribution and wishes him well in his future footballing career.