Goals from Gary Hooper, Theo Robinson and Simon Johnson - coupled with a defeat for Stockport - were enough to give the Bulls League One football next season.
The result never looked in doubt from the minute Hooper rounded Bees keeper Ben Hamer to strike home into the far corner on 18 minutes.
Robinson made it two nine minutes before the break when he raced on to a defensive blunder to skip past the Brentford defence and finish coolly from 10 yards.
That decisive goal came just a minute after Robinson had been denied from the penalty spot by Hamer after a hotly disputed foul.
Brentford's Glenn Poole came closest for the Londoners with a superb free-kick which cannoned to safety off the bar and from the break that followed Johnson wrapped it up with a last-minute strike.