The teenager, on as a second half substitute, scored with a low 25 yard drive on the hour mark to settle a low key encounter at Oakwell.
With nothing at stake for either club, there was inevitably an ‘end of season’ feel about the game for long periods.
Millwall, whose bid for play-off qualification ended last weekend, initially looked the better side, but Barnsley improved after halftime and just about deserved the win.
The Tykes had shown only glimpses of real hunger in the first half; Bobby Hassell poked a half chance wide, Stephen Foster headed over from a Kieran Trippier freekick, and a Jason Shackell header was clawed from under the bar by goalkeeper David Forde.
Things came to life in the second half with chances at both ends.
Tamika Mkandawire struck the post with a header for Millwall deep into stoppage time.
Barnsley’s victory means they finish 17th in the table, beating last season’s performance by one position and two points.
There was a hefty police presence at the final whistle which stopped Millwall fans, but not Barnsley’s, from invading the pitch.
Click on the external link on the right of the page to follow the action with our Match Centre service. And for the best reports, pictures and analysis, read Sports Monday inside your Yorkshire Post.