Abdellatif Merdass, an MP for the opposition Constitutional Union, was gunned down outside his home in Casablanca, Abdellah Ferdous told Anadolu Agency.
He said motives behind the killing remain unknown.
Moroccan authorities have yet to comment on the murder.
Founded by then prime minister Maati Bouabid in 1983, the Constitutional Union is a liberal conservative party aligned with the monarchy in Morocco.
It contested all parliamentary elections in Morocco until 1998.
When the opposition came to power in 1998, the party then moved to the ranks of the opposition.