Goals from James Hanson, Rory McArdle and Nahki Wells earned Bradford promotion as the Cobblers were brushed aside in an entertaining clash in the capital.
After the match, Parkinson told Sky Sports: "We had a great first half, three goals is a dream start for us and in the second half we were very professional.
"Northampton are a strong team and a good side but today I thought we were excellent and we deservedly won the game.
"This is more important (than the League Cup final) because obviously it determines the future of the club.
"The League Cup - it was great to get to the final with the revenue it brought in, but this is what it is all about, this is the bread and butter and to get this club back in the first division is a dream for us all and now we can enjoy it, enjoy the summer and prepare for next year."
On his team's character, he added: "This was our 64th game of the season, to put in a performance like we did today, enormous credit goes to the lads, they have been outstanding and if any group of supporters deserve success, it's the Bradford fans."