The 22-year-old left the Gladiators in the summer to join the Nottingham-based club but was released last week, shortly after former Steve Kittrick parted ways with the club.
Cartwright goes straight into the squad to face Bedford Town at home in the FA Trophy third qualifying round on Saturday.
Matlock boss Martin Carruthers said: “I’m delighted to have Ethan back with us. He was someone we didn’t want to lose in the summer.
"Circumstances change and Ethan himself was keen to come back. He’s a great lad - he’s got energy, legs, he works hard and he’ll be a great boost to the midfield area.
"He was welcomed back at training on Thursday and I’m really looking forward to working with him.”
The Gladiators could also welcome back Alex Duhameau this weekend.
He has yet to feature in 2023/24 after picking up an injury in pre-season but could be in-line for a long-awaited return.
Photo credit: Basford United