The Adelaide Strikers' pace ace was diagnosed with a disc injury following her participation in the Australia A tour of India last month.
It was initially hoped a period of de-loading would allow Brown to recover in time for the WBBL season, which runs from October 29 to December 5.
But Cricket Australia confirmed on Monday the injury hadn't healed sufficiently to allow Brown to resume training.
The news is a big blow to Brown, who was dropped ahead of this year's T20 World Cup and was looking to win back her spot in time for the T20 Champions Trophy in India from February 14-28.
The back injury also ruled the 23-year-old out of Australia's recent 3-0 ODI clean sweep of Bangladesh.
Brown, who has clocked 127.2km/h on the speed gun, has played six Tests, 30 ODIs and 41 T20s for Australia, and will be a huge loss for the Strikers this WBBL season.
"Darcie is a quality player who will be missed on the field, but she remains a hugely important part of our squad," Strikers coach Luke Williams said.
"She brings outstanding experience, professionalism and leadership, and those qualities will continue to have a positive influence on our group throughout WBBL 12."
Australia are 1-0 up in their three-match T20 series against New Zealand after posting a tense two-wicket win at North Sydney Oval on Sunday.
Games two and three will be held at North Sydney Oval on Tuesday and Thursday.
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