The 19-year-old all rounder, who made her Australian debut in September, was ushered into the role with a smoking ceremony in Tasmania two days out from the Thunder's season opener against Adelaide.

Darlington was not a shock choice for the captaincy despite her age, having led NSW as the state's youngest ever captain at Women's National Cricket League level last summer.

She replaces Haynes who has opted out of this summer's WBBL following the birth of her son Hugo.

"It's a huge honour I've been a part of this club for nearly five years now and supported it all the way through," Darlington said.

"To have this opportunity to step in for Rach, she's been a massive influence in definitely my leadership style. It's a big loss to lose one of the best players in the world and our leader, that's the most crucial part.

"It was actually an amazing experience to captain the Breakers, another dream come true I could say. I definitely learned a lot during that experience and just knowing that I'm willing to make those decisions and be able to lead from the front.

"It definitely was a bit learning curve but it's prepared me quite well to take the Thunder reins."

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Meanwhile Sydney Thunder coach Trevor Griffin has backed Meteors quick Olivia Porter to play a key role in his side's Women's Big Bash title defence, which begins on Saturday against the Adelaide Strikers.

Porter missed all of last season with a leg injury, heart-breakingly diagnosed just days out from last summer's WBBL, which the Thunder won.

But Griffin has stuck strong with Porter, and offered her a two-year contract extension earlier this season despite the 19-year-old still waiting to debut.

"I'm really excited by Liv, I was bitterly disappointed for her last year," Griffin said.

"She's such a young talent, she's fought back from her injury, she's worked incredibly hard over the preseason and she's good to go.

"She certainly will be up there fighting for a place within that starting 11. She's a determined character, she knows what she wants, she works hard and she certainly wants to be putting pressure on other players and making a start for the Thunder."

Porter was diagnosed with a tibial stress reaction on the eve of last season's WBBL, played in a Sydney bubble as a way to combat the COVID pandemic. Despite the frustration of the injury, she stayed with her teammates.

"We couldn't fault the way she handled it, for somebody so young to have that setback she handled it like a proper pro," Griffin said.

"One thing I can remember saying to her is that the best players don't get to the top on a straight line, the best players get to the top by going through moments of adversity, a loss of form, being dropped, big injuries.

"That's part of being a professional cricketer and it's how you respond and how you come back from those, how it all makes you a better person, not just a cricketer.

"It's also about developing Liv as a person and she's a cracker already and I can't wait to get up to Tassie and be around her and seeing how much she's progressed over the last 12 months."

Griffin has been forced to make several changes to this title-winning squad from last season. He has brought in Indian pair Smriti Mandhana and Deepti Sharma, and English young gun Issy Wong.