Goals from Tom Adeyemi and Marcello Trotta in either half at Griffin Park saw the Bees record their first win in eight games to stay in the play-off places.
Adeyemi put the Londoners ahead just before the break when he cut in from the left to send a rasping drive into the far corner from the edge of the box.
Trotta made sure of the points late on with a sublime curling effort from the corner of the penalty area after a great ball from Adam Forshaw.
The Italian almost made it three seconds later but saw his clever near-post flick blocked at point-blank range by Stevenage 'keeper Chris Day.
Brentford should have wrapped it up by half-time but Paul Hayes squandered two gilt-edged chances to make the scoreline more emphatic.
He twice sliced wide in the early stages when clean through as Brentford tried to make the early breakthrough.
The visitors barely threatened Simon Moore in the Brentford goal, the closest effort a Sam Hoskins header easily saved.
Harry Forrester tested Day with a curling effort which lacked power late on and Clayton Donaldson blazed over deep into injury-time.