West Brom will play local rivals Wolves in the play-offs as Kevin Phillips' hat-trick powered Albion to victory.
Phillips' close-range finish put West Brom ahead, while Nathan Ellington made it 2-0 with a penalty, before he got a second with a clever individual effort.
West Brom added a fourth before the break when Robert Koren scored with a superbly executed left-footed flick.
A powerful shot and an incisive finish sealed Phillips' hat-trick, while Zoltan Gera swept home the seventh.
Koren set the tempo for West Brom in the opening minutes when he manoeuvred himself some space on the edge of the box, before going close with a rising shot.
Barnsley goalkeeper David Lucas briefly stemmed the West Brom onslaught, turning Sam Sodje's header over the bar and bravely coming out to claim a Koren cross.
But there was nothing Lucas could do about West Brom's opener on 20 minutes.
Barnsley failed to cut out Paul McShane's cross from the right and when the ball deflected through to Phillips, the former Southampton striker turned swiftly to shoot past Lucas.
West Brom extended their lead through Ellington's penalty after youngster Luke Potter fouled Koren.
Ellington claimed his second goal after he flicked the ball over Bobby Hassell's head and then rifled the ball past Lucas.
West Brom were 4-0 up at the interval thanks to Koren's superbly executed goal as the Slovenia scored with a flick when both his feet were off the ground.
Their play-off place all but guaranteed West Brom could have been forgiven for taking it easy in the second half, but Phillips had more goals on his mind.
First he unleashed a shot past Lucas, completing his hat-trick with a side-footed finish.
Substitute Gera had played a key role in Phillips' third goal and the Hungarian got West Brom's seventh when he drilled the ball into the corner of the net.
West Brom: Kiely, McShane (Hodgkiss 46), Perry, Sodje, Robinson, Greening, Chaplow, Koren, Koumas (Gera 54), Ellington (MacDonald 62), Phillips.
Subs Not Used: Daniels, Albrechtsen.
Booked: McShane.
Goals: Phillips 21, Ellington 25 pen, 36, Koren 40, Phillips 53, 71, Gera 75.
Barnsley: Lucas, Austin, Atkinson, Potter, Hassell, Devaney (McCann 57), Howard, Togwell (Heslop 63), Kyel Reid, Nardiello, Ferenczi (Rajczi 57).
Subs Not Used: Colgan, Heckingbottom.
Booked: Howard, Nardiello, Kyel Reid.
Att: 23,568
Ref: L Probert (Gloucestershire).
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