Dew will serve as the senior assistant to his 2004 Power premiership teammate Carr, with the responsibility of leading the club's midfield.
The 46-year-old, who was axed after almost six seasons as Gold Coast's senior coach in 2023, joined the Lions as an assistant to Chris Fagan last year and played a key role in back-to-back premierships.
Dew, who played 180 games for Port Adelaide and 26 with Hawthorn, including their 2008 premiership, said he is eager to get started in his new role.
"I couldn't be more excited to be heading back to my former club as a senior assistant coach," Dew said in a Port Adelaide club statement.
"To work alongside my old teammate Josh Carr is a great opportunity, and one I am really looking forward to.
"I have great respect for Josh and his vision for the club moving forward, and the Port Adelaide playing list is full of talent."
After finishing his decorated playing career in 2009, Dew served as a development coach and assistant at Sydney for eight years, helping guide the Swans to the 2012 premiership under John Longmire.
Dew was a specialist coach under Fagan in 2024 and took over the Lions' forward-line this year, remodelling the group after the departure of key figure Joe Daniher.
"While you never want to lose great people like Dewy and an assistant coach with his invaluable experience, we fully understand his decision," Brisbane football manager Danny Daly said.
"In his two seasons with the club, Dewy was a vital part in our premiership success and became a much-loved staff member.
"On behalf of everyone at the Brisbane Lions we would like to thank Dewy and his family for their contribution and wish them all the best."
Carr has taken over from Port Adelaide's longest-serving AFL coach Ken Hinkley, who stepped down at the end of the 2025 season.
Dew is the latest addition to Carr's revamped coaching group, joining new assistant coaches Luke Webster and Darren Reeves, and director of coaching Andy Collins.
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