Wicketkeeper Max Chu helped clinch the win with an impressive effort behind the stumps and some clutch batting at the depth.
He effected two stumpings and collected a brace of run outs.
The left-hander also clobbered a delivery from Scott Kuggeleijn over backward square for six in the final over.
Angus McKenze supplied the coup de grace. He got a junk half-tracker down leg and helped it on its way over the fine leg boundary.
Northern had posted 146 for eight on a slow surface at the University Oval.
Otago looked to be on track to overhaul the target easily enough.
Neil Broom anchored the chase with 62 and Llew Johnson played an excellent cameo, clubbing 25 from 13 balls just when the innings needed a spark.
But neither could see the task through, which left Chu and McKenzie to finish the job off.
Earlier, Otago part-time spinner Josh Finnie struck a double blow to help put the visitors under pressure midway through their innings.
The Brave had got through to a useful 95 for two in the 12th over.
Katene Clarke and Henry Cooper had put on 42 at quicker than a run a ball.
Clarke had blasted 49 but was caught on the boundary.
Cooper (24) went very next ball. He got a little unlucky.
The ball whizzed past his bat. Chu fumbled but the rebound crashed into the stumps, catching Cooper short of his ground.
Finnie was on a hat trick. Peter Bocock survived it, but did not last.
He was part of the next clump of wickets to tumble.
This time it was Michael Rippon who got two in a row.
Colin de Grandhomme predictably took on the big boundary and lost, and Bocock was trapped lbw.
Northern had lost four wickets for nine runs.
McKenzie bowled a tight final over to help keep the Brave under 150.
Otago bowled 12 overs of spin. Finnie (two for 22), Rippon (two for 27) and Anaru Kitchen with one for 19 all had a big impact.
But Chu was the star. The 21-year-old is a very slick keeper but his 10 not out at the end proved incredibly valuable in the context of the game.
The Volts are home again tomorrow, playing Canterbury in a Ford Trophy game.
