Sussex finally clinched the Division Two title thanks to Glamorgan's failure to beat Surrey at Lord's.
After earning promotion on Wednesday, they were overwhelming favourites to clinch the title once they had beaten Northants at Hove.
If Glamorgan had won at The Oval, Sussex would have gone into next week still needing three more points.
But Glamorgan were forced to settle for a draw, allowing the champagne corks to pop at Hove with a game to spare.
Sussex will still play a part in the promotion race next week.
They travel to New Road to face third-placed Worcestershire, who can still go up if they beat Sussex and make up a nine-point gap on Glamorgan, who are at home to bottom club Derbyshire.