Following weeks of speculation, the reigning wooden spooners confirmed on Tuesday that Flintoff had signed a two-year deal to replace Trevor Bayliss.
Known ubiquitously as 'Freddie', Flintoff is remembered for his prolific career as an allrounder that yielded 272 international caps across all formats.
He was notably crowned player of the 2005 Ashes series, when England clinched the storied urn for the first time since the summer of 1986/87.
As a coach, Flintoff led England Lions on tour of Australia over the summer and also Northern Superchargers, now known as Sunrisers Leeds, for two seasons of The Hundred.
Under Flintoff's leadership, the Superchargers surged from wooden spooners in 2023 to semi-finalists two seasons later.
He will continue to coach England Lions, who are currently playing a multi-format series against South Africa A, while in charge of the Thunder.
Flintoff's Thunder deal marks his return to the BBL for the first time since his final season as a player ended in 2015.
"I can't wait to get over there and get started," Flintoff said.
"You look around the world now and everyone gets the opportunity to play for all different teams but one of my aims over the time with Sydney Thunder is that every player looks back thinking "that's the best part of the year, that's a team that I want to play for."
Flintoff inherits a Thunder squad that boasts plenty of talent, including former Test players Sam Konstas, David Warner and Cameron Bancroft, English wicketkeeper Sam Billings and white-ball international Tanveer Sangha.
The Thunder managed just two wins in a dismal 2025/26 campaign, though, thwarted by a lack of firepower with the ball.
Only one Thunder bowler ranked in the top 25 for most wickets taken last summer.
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