Barlow, who also had the top job at Chesterfield, will be No.2 to Chris Hutchings at the JJB Stadium.
Barlow also had caretaker spells in charge of Hull City and Nottingham Forest, but has been out of work since October when he left the Tigers.
"Frank was always my first choice, and I'm delighted we have got him on board," said Hutchings.
"I need someone I can trust implicity, and when it comes to football knowledge you can't really get more experience than Frank.
"He knows players inside out, what motivates them, and how to get the best out of them."