Pompey twice fought from behind to beat Barnsley and secure promotion to the Championship.
The dramatic 3-2 victory at a jubilant Fratton Park also meant that they secured the League One title.
Devante Cole and John McAtee had twice given the visitors the lead, only for John Mousinho's men to hit back through Kusini Yengi's strike and a Colby Bishop penalty.
And with time running out, Conor Shaughnessy headed home a corner to get the south coast party started.