The match was reduced to 12 overs per side and started one hour 10 minutes late after persistent rain on Saturday.
Sixers opener Josh Philippe hit a superb 52 off 29 balls to help his side post 116-5.
The Stars struggled in reply, losing key men Marcus Stoinis and Glenn Maxwell early as they made only 97-6.
It is the Sixers’ first title since winning the inaugural Twenty20 competition in 2011-12, while the Stars have now lost all three of their Big Bash finals.
- How the final unfolded
Sixers wrap up emphatic win
After a terrific effort by the SCG groundstaff to get the match on following heavy rain, the Stars looked to have the advantage by winning the bat flip and bowling first on a tricky pitch for scoring.
England’s James Vince struggled as he chipped to mid-on for two before Philippe and Australia batsman Steve Smith started to find the boundary.
Once Smith holed out for 21, Stars spinners Adam Zampa and Maxwell reduced the hosts to 68-4, but a vital stand of 48 between Jordan Silk (27 not out) and Philippe, who hit three sixes, led the Sixers to what seemed to be a par total.
Stars opener Stoinis set the record for the most runs in a single edition of the Big Bash this year (705) and he started ominously with a four and six off Australia off-spinner Nathan Lyon in the first over of the reply.
But Stoinis picked out deep square leg off his fourth ball, before fellow opener Nic Maddinson tamely lofted the superb Josh Hazlewood to Vince for a duck and Maxwell was trapped lbw by Steve O’Keefe for just five.
The reeling Stars fell into complete disarray at 25-4 when Peter Handscomb was carelessly run out by Smith attempting a second run that was never on.
Despite some defiant late hitting by Nick Larkin (38 not out) and Nathan Coulter-Nile (19 not out), the visitors never threatened the target.
The Sixers would have been awarded the title had the match been abandoned after winning the right to host the final by beating the Stars, who had topped the group stage, in the earlier qualifier round.
But captain Moises Henriques said he was much happier his side had to “get out there and do some work to win the trophy” after they wrapped up an emphatic victory shortly before the rain returned.
England stars impress in 2019-20 tournament
The final was the culmination of seven weeks of competition between eight sides in the ninth edition of the BBL, with the campaign shortened in length from last season but with two matches added, taking the total to 61.
Several England players starred in the tournament, with Tom Curran having taken 22 wickets for the Sixers before joining up with England in South Africa.
Alex Hales, who is hoping to force his way back into England white-ball reckoning after being dropped from the World Cup squad for disciplinary reasons, scored the second most runs after Stoinis – 576 – before his Sydney Thunder side were beaten by the Stars in the challenger round.
Batsman Liam Livingstone impressed by hitting 425 runs in his debut season at Perth Scorchers, while team-mate Chris Jordan took 15 wickets in 13 matches.
Tom Banton lit up the early stages of the tournament, with three half-centuries for Brisbane Heat, including a 16-ball 50 in which he hit five sixes in an over, before joining Jordan and Curran in South Africa.