Glamorgan resumed their second innings on 164 for six - requiring another 67 runs to make the hosts bat again.
Northamptonshire's attack - spearheaded by Carl Greenidge - finally dismissed the visitors for 312, to leave their batsmen a victory target of 82.
Robert White blasted a 41-ball half-century - his second of the match - and the hosts raced to victory in just 17.1 overs.
Glamorgan advanced their overnight total to 183 before Northamptonshire made their first breakthrough with Robert Croft (14) playing down the wrong line to a good-length ball from left-arm spinner Monty Panesar to be trapped leg before.
When Andrew Davies (six) was bowled by off-spinner Graeme Swann with the total on 202, Northamptonshire must have scented an innings victory but Mike Kasprowicz and Dean Cosker put on 58 in a breezy ninth-wicket stand.
Cosker hammered 36 from only 25 balls before he was bowled playing across the line by Greenidge. He hit five fours and one six - an impressive pull over deep midwicket off Swann.
Yet another half-century stand between Kasprowicz and Simon Jones (17) took Glamorgan past the 300-mark before Greenidge finally wrapped up the innings by having Jones caught behind by wicketkeeper Tobin Bailey.
Kasprowicz was left unbeaten on an impressive 72 - just one short of his previous championship best. His mixture of attack and solid defence yielded seven fours and a six from 96 balls faced.
Greenidge finished with three for 68 for match figures of eight for 112 while Panesar and Swann captured three wickets apiece.
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