In a low-scoring game on a slow pitch, McCullum smashed 18 from five balls, striking two sixes and a four as Glamorgan chased down 119 to claim a four-wicket win with five balls to spare.
The victory kept up Glamorgan's 100 per cent record and put them top of the Midlands, Wales and West Group after they beat Worcestershire last week.
Glamorgan, who were without all-rounder Jim Allenby with a stomach problem, put Warwickshire into bat and restricted them to 118 all out, with Rikki Clarke top-scoring with 42 from 41 balls. Graham Wagg finished with three for 24.
Veteran all-rounder Azhar Mahmood held his nerve to help Surrey clinch a tense three-run win over Sussex in a low-scoring thriller in front of a 12,000 crowd at the Kia Oval.
With the Sharks requiring 12 for victory from the final over, Mahmood, playing in his 181st t20 match, restricted the visitors to eight to secure Surrey's third successive South Group win.
In pursuit of 140 for victory under the floodlights, Sussex slipped to 11 for three and were reliant on a 33-ball 46 from Scott Styris, but it wasn't enough.
Gary Wilson's unbeaten 44 from 37 balls helped Surrey post 139 for six.
- Sports & Recreation
- Azhar Mahmood