The visitors rarely threatened the home goal in a first half dominated by the Bees.
But it was not until the 71st minute that the Londoners made their possession count, Charlie MacDonald slamming home from the penalty spot after the referee spotted a handball by Terriers captain Peter Clarke in the box.
Just over 10 minutes later it was two as Lewis Grabban raced onto a through ball to fire a rasping drive across Town keeper Alex Smithies.
A minute later and it was all over as MacDonald juggled the ball twice on his thigh before turning sharply and drilling home into the far corner on the volley.
Huddersfield squandered the chance of an injury-time consolation when Gary Roberts blazed over from the penalty spot after Brentford goalkeeper Wojciech Szczesny fouled him in the box.