Millwall captain Paul Robinson has fired the club back into the Championship.
The centre-back, whose recovery from a broken metatarsal meant he only started last season's 3-2 final defeat to Scunthorpe on the bench, smashed home from close range after Danny Schofield's corner had found its way through.
His 39th-minute goal was nothing less than the Lions deserved having posed the bigger threat throughout against a Town side who saw Charlie Austin slice wide a golden opportunity to level matters when clean through in the second half.
The victory - in front of 73,108 fans - went some way to banishing the memory of five previous play-off defeats for Millwall, who were left celebrating a return to England's second tier following their relegation in 2006.