Phil Parkinson's side headed into the game at Oakwell seventh in the table, but they remained there as Barnsley took the points.
Bradford began the game brilliantly, Jason Kennedy sliding home to open the scoring after just 44 seconds.
Barnsley found a response immediately after half-time, however, as Rory McArdle headed Conor Hourihane's free-kick beyond his own goalkeeper undre pressure from Lewin Nyatanga.
The hosts took the lead midway through the second period, Sam Winnall converting Nyatanga's cross at the near post to finish off a fine move.
And the gloss was added in the dying moments when Kane Hemmings netted just after coming off the bench.
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