A new finals system
After the sprawling 2018-19 season, Cricket Australia kept the 56-match league stage but changed everything after it. The four-team knockout was replaced by a five-match finals series borrowed in principle from Australian rules football: the fourth and fifth sides met in an Eliminator, the top two in a Qualifier, the third side played the Eliminator winner in a Knockout, the Qualifier loser played the Knockout winner in a Challenger, and the Qualifier winner met the Challenger winner in the Final. The top two therefore had two chances to reach the final, and the fifth-placed side had to win four matches to lift the trophy.
The season ran from 17 December 2019 to 8 February 2020 and was played against the background of the Australian bushfire summer, which affected air quality at several venues.
Stoinis and Sams
Marcus Stoinis had a season without precedent in the competition. He made 705 runs for Melbourne Stars, the first man to pass 700, and on 12 January at the Melbourne Cricket Ground he made 147 not out against Sydney Sixers in a total of 219 for 1, the highest individual innings in Big Bash League history. He was named player of the tournament.
Daniel Sams of Sydney Thunder took 30 wickets, also a record, and made useful runs down the order. Matthew Wade's 130 not out for Hobart at Adelaide Oval and Aaron Finch's hundred for the Renegades were the other large innings of the summer.
The finals
Melbourne Stars finished first, Sydney Sixers second, Adelaide Strikers third, and Hobart Hurricanes and Sydney Thunder took the last two places on identical records.
Sydney Thunder won the Eliminator at Blundstone Arena by 57 runs, then beat Adelaide Strikers by eight runs in the Knockout at Adelaide Oval. In the Qualifier at the Melbourne Cricket Ground, Sydney Sixers made only 142 for 7 but bowled Melbourne Stars out for 99, Steve O'Keefe taking the award. That put the Sixers straight into the final and sent the Stars to the Challenger, where they made 194 for 2 and beat Sydney Thunder by 28 runs.
The final
Rain reduced the final at the Sydney Cricket Ground on 8 February to twelve overs a side. Sydney Sixers made 116 for 5, Josh Philippe scoring the bulk of it and taking the match award. Melbourne Stars finished on 97 for 6, 19 runs short. It was the Sixers' second title, eight years after their first, and the third final Melbourne Stars had lost in five seasons.
Afterwards
The five-team finals series was kept for three more seasons before the league stage was cut to 40 matches in 2023-24 and the finals to four. Stoinis's 147 not out stood as the competition record until Glenn Maxwell passed it in 2021-22, and Sams's 30 wickets was matched by Peter Siddle in the same season.