Barnsley had to settle for second place in Sky Bet League One after losing 2-1 to Bristol Rovers at the Memorial Stadium.
The visitors took a 12th-minute lead when Mamadou Thiam's header at the far post from a right-wing cross was parried by Rovers goalkeeper Adam Smith into the path of Kieffer Moore, who nodded home from close range.
But Barnsley were reduced to 10 men just before the break when central defender Liam Lindsay, booked after 37 minutes for a foul, was shown a second yellow card for pulling back Alex Rodman as he looked to break clear on the right.
It was Rodman who fired Rovers level after 71 minutes, shooting home off the underside of the crossbar after his first effort had been parried by Adam Davies.
And the right-sided midfielder struck again in injury time, volleying in at the far post from a Liam Sercombe cross.
Luton's 3-1 win over Oxford United means they are the Sky Bet League One champions.