The 22-year-old spent last season on loan with Ligue 2 side Chateauroux - his third spell outside Allianz Riviera Stadium outfit - and made 34 appearances across all competitions scoring 12 goals.
The addition of the attacker will be expected to bolster the Bees’ squad as they aim for promotion after finishing three places adrift of the playoff spot last term.
Rasmus Ankersen, club's co-director, is delighted with the new recruit and is confident that he will ‘cause many Championship defenders problems.’
“Said is a player with lots of potentials,” Ankersen told club website.
“He has the pace and technical skills to cause many Championship defenders problems, and we are pleased that it was possible to sign him early in the window so he can now go with the rest of the team to the pre-season camp."
Benrahma could be involved when Brentford clash with Wycombe Wanderers in a pre-season tie on July 17.