An unbeaten ninth-wicket partnership of 99 in 10 overs between Murray Goodwin and Mohammad Sami handed Sussex the NatWest Pro40 Division One title.
In an unbelievable finish, with three needed off the last delivery bowled by Charlie Shreck, Goodwin launched the ball over long-on for six to spark wild celebrations among the travelling Sussex supporters.
Nottinghamshire had seemed bound to win their first one-day trophy in 19 years after posting 226 for seven, with Samit Patel making 78.
Patel (three for 36) then combined with Graeme Swann (three for 33) to tear through the Sussex middle order, reducing the visitors to 130 for eight, before Goodwin smashed 87 not out off 64 balls, with Sami making an unbeaten 32 to add to opener Mike Yardy's 53.
The two sides went into the game knowing the victors would be crowned as champions and it was Sussex who struck first with Sami bowling Swann off the fifth ball of the match.
Sami's opening partner James Kirtley followed up with the wicket of Mark Wagh, caught at point, but Patel then arrived at the crease to settle any nerves.
The right-hander began steadily before opening his shoulders after Will Jefferson was bowled, reaching his half-century off 61 balls.
He survived a caught and bowled chance off Mike Yardy on 59 and hit two sixes over cover before holing out at long-off as the Outlaws looked to accelerate.
Prince was content to give Patel much of the strike but eventually reverse-swept to short third man, while Bilal Shafayat was fooled by Kirtley's slower ball and Mark Ealham was yorked.
Andre Adams smashed two sixes to provide a late boost to the Nottinghamshire total as 26 runs came off the last two overs.
England wicketkeeper Matt Prior and all-rounder Luke Wright fell cheaply at the start of the Sussex innings before Yardy's accomplished 53.
But he was undone by the turn of Patel in the left-armer's first over, sparking a collapse as six wickets fell for 43 runs.
The game seemed done and dusted when Robin Martin-Jenkins pulled Patel straight to midwicket but Sami showed tremendous poise to support veteran Goodwin in the chase.
Having seen off the spinners, the pair chanced their arms against the Nottinghamshire seamers and kept on finding the gaps to keep up with the required run-rate of 10 an over.
It all came down to the final over with 15 needed for the tie which would ensure the Division One title for Sussex.
And after Goodwin had found the midwicket boundary and Sami edged to third man for four, the Zimbabwean stepped back in his crease to finish the game in amazing fashion.