The Wigan Athletic legend was assistant to Caldwell with the Latics.
He said: “I’m delighted to be here. I’ve had a good working relationship with Gary and we’ve always kept in touch.
“On matchdays, I’ll be up above in the stand watching the game and provide input. I’ll also help Guy Branston with recruitment.
“The set-up here is great and it’s all geared for success. I’ve got a wide range of experience so I hope to make a valuable contribution.”
Caldwell, who is already assisted by former Manchester City and Huddersfield coach Steve Eyre, is delighted to strengthen his backroom staff.
“I have 100 per cent trust in Graham and I value his opinions,” he said.
“He has great knowledge at every level of the game. He will be a great help to me in various ways, including preparing for matches and signing players.”
Barrow was a player, coach, assistant manager and caretaker manager at Wigan and also managed Chester on two occasions, Rochdale and Bury.
The 63-year-old left Wigan in May.