Sydney Thunder have re-signed Alex Blackwell and Rachael Haynes for the upcoming season of the Women's Big Bash League, with the latter named captain after Blackwell opted out. While Blackwell has signed a year's contract with the franchise, Haynes' deal extends to two years.

The extension means that 35-year-old Blackwell, who is also Thunder's all-time leading run-getter, will be playing a record-equalling 19th season of domestic cricket. She will join West Australian Lauren Ebsary as the longest-serving Australian domestic female player, since women's players went to a full season with the creation of the Women's National Cricket League in 1996-97.

"Continual improvement as a batter and team member is what I always look to achieve," Blackwell told cricket.com.au. "This season I will be juggling more responsibilities away from the playing field and I'm confident this will enhance my enjoyment of playing the game."

The other responsibilities Blackwell mentioned are to do with her position as director on the Cricket New South Wales board and her job as an associate genetics counsellor at Sydney Children's Hospital.

"It's a great foundation Alex and Jo [Broadbent, NSW Breakers mentor] created and I am looking forward to continuing that on," Haynes told AAP. "It's something I've done throughout my career and I'm comfortable in my ability to lead the team.

"Alex was really supportive about me taking over. We're really happy she has decided to go another year, her presence will be really good to have around the group."

Sydney Thunder will begin their campaign in the first-ever standalone WBBL with a derby clash against Sydney Sixers on October 18.