The Sixers were reeling at 3-6 in the third over but Gardner (124 off 60) and England's Alice Capsey (54 not out off 40) put on a mammoth fourth wicket stand of 176.
Gardner's dismissal triggered a late collapse, with the Sixers losing 5-7, but they finished at 8-196.
It was the third straight WBBL innings record score in Sunday's double-header, after Brisbane made 5-178 and Sydney Thunder reached their target with six wickets and 20 balls to spare.
Defending champions Hobart could muster only 109 in response to the Sixers' mammoth total, and were never in contention after slumping to 5-26 in the eighth over.
They dropped to 0-2 for the season and the Sixers moved to 2-0.
Gardner's ball striking was of the highest order as she belted 10 fours and nine sixes - most of them over the leg side boundary.
"I felt like this is a really good wicket. The start probably didn't show that but I just think if you gave yourself a chance, there was certainly plenty of runs to be scored out there," Gardner told Seven, Fox and Kayo, after hitting her second WBBL century and highest T20 score.
Spinner Gardner (3-22) also made a major contribution with the ball and combined with highly regarded 17-year-old quick Caoimhe Bray to destabilise the Hurricanes.
They lost 5-9 in 20 balls with the impressive Bray (2-14) starting the collapse by dismissing Chamari Athapaththu and Rachel Trenaman in her third over.
Gardner struck with her first ball, having the dangerous Lizelle Lee caught, and bowled opposing captain Nicola Carey five deliveries later.
She returned to bowl Chenille Henry (32 off 20), with Maddy Green (42 not out off 33), the only other Hurricanes batter to offer resistance.
Only Grace Harris had previously scored a century and taken at least three wickets in a WBBL game. Spinner Melie Kerr (3-25) swept through the tail.
Earlier on Sunday, the Thunder made light of their largest ever run chase reaching the target with 20 balls to spare.
Georgia Voll fell for two, but Thunder's other's power hitters prospered against an attack which failed to execute under pressure and bowled too many loose deliveries.
Phoebe Litchfield (41 off 19) provided the early spark with some scintillating strokes and England veteran Heather Knight (54 not out off 29) paced the chase with a typically smart innings.
She put on 63 with Anika Learoyd (37 off 28) and 59 with Laura Harris (35 off 16), who was caught by her sister Grace with three needed for victory.
Thunder made it two wins from as many games.
Grace Harris (58 off 37) and Georgia Redmayne (57 off 44) put on 99 for the second wicket, carrying Heat to 1-118 in the 14th over.
Orla Prendergast (28 off 20) chipped in during the final overs but Brisbane couldn't find an extra gear, with Thunder striking six more fours than the visitors.
Brisbane's drought since their last win stretched to 12 games and 702 da
