Duncan, a former captain of Brisbane Roar's youth team, has the traits to make an instant ALM impact, according to Glory coach Ruben Zadkovich.
"Zach is a player that has a lot of positive attributes ... he is a natural ball-winner and has the technical ability to match," Zadkovich said in a statement on Tuesday.
Perth's head of recruitment Andy Keogh said the Glory were "over the moon" to secure Duncan on loan.
"AGF rate him very highly and I'm delighted they have agreed for us to help develop their player," Keogh said.
He made his A-League debut in March 2019 and scored his maiden senior goal a month later before being signed by AGF.
Perth's first fixture of the new ALM season is on Oct. 9 against Western Sydney.