The 18-year-old, who impressed selectors in last summer's Breakers campaign, is fast developing a reputation for her big hitting.
Gardner says she is looking forward to working alongside some of her idols, including national team star Ellyse Perry.
"...All the girls that have been joining the Sixers are some of my idols," she said.
"I do look up to Pez [Ellyse Perry], she's a very good player and of course, because she plays for Australia."
The Sydneysider made history earlier this year when she became the first female winner of the Lord Taverners Indigenous Cricketer of the Year award, in addition to taking home the Women's Player of the Tournament award in the Imparja Cup.
Sixers WBBL Coach Ben Sawyer is confident Gardner will make her mark on the first ever Women's Big Bash league.
"Ash is a hard-hitting batter and an attacking off spin bowler and is sure to play a big role in WBBL 1," said Sawyer.
The Sixers are yet to announce their complete WBBL squad list but Alyssa Healy, Emily Leys, Perry, Lauren Smith and Lisa Sthalekar have been confirmed so far.