At the County Ground in Northampton, the home side batted first and made 146-5 in their twenty overs.
Chris Woakes took 3-21 in 3 overs for Warwickshire whilst Alex Wakely top scored with 41 from 31 balls including the only six in Northamptonshire's innings.
Faced with a relatively easy target, Warwickshire still smouldering from the County Championship defeat at Yorkshire needed to ensure they got the win.
Neil Carter cracked two fours before being caught by Vaas at the end of the first over but a stand of 77 between Darren Maddy and Keith Barker moved the score along. Maddy was out for 30 after giving wicketkeeper O'Brien a catch followed by Barker who had made 46 from 28 balls being caught by Hall.
Jim Troughton went a run later, but Ian Westwood (24 not out) and Tim Ambrose (30 not out) steered Warwicks to a six wicket victory.
Warwickshire are back in Twenty/20 action with a home game against Yorkshire on Wednesday. PLay is due to start at 5.30pm. Please note that tickets bought after 12 noon on the day of a game rise to £25 for adults.