Turner spent the last year on the Demons' list after being recruited out of the VAFA and VFL, having played for Old Haileybury and Frankston before gaining the attention of Melbourne.
The 21-year-old was signed through the Supplemental Selection Period and would just six games for the Casey Demons due to a season hampered by a groin injury.
After not being offered a new deal by the Demons for 2024, Turner has returned to the VFL through signing with Port Melbourne.
The Borough confirmed the acquisition of the key defender on Thursday, expressing their excitement to have the Turner join their ranks.
"21 year old Turner played 14 games in 2022 for Old Haileybury in the VAFA and twice for Frankston in the VFL before being invited to train with Melbourne AFL program over the summer period, where he impressed and was subsequently signed by the Dees in February on the final day of the AFL pre-season supplemental selection period (SSP), Playing 6 games for Casey Demons in an injury interrupted season.
"Borough fans can expect to see Kye's versatility, speed, ability to intercept and a desire to take the game on from defence will no doubt challenge opposition forwards.
"We welcome Kye Turner to the Borough."
The Borough managed just six wins in 2023 to finish 15th on the VFL ladder.