With 100 days to go before co-hosting the World Cup with New Zealand, the Matildas returned to winning ways after their friendly defeat by Scotland on Friday thwarted a seventh straight win.
Kerr opened the scoring in the 32nd minute capitalising on a poor clearance by defender Leah Williamson (26) to coolly slot home, despite appearing to be offside as there was no VAR in place.
Australia's counter-attacking play paid off and Grant doubled the lead in the 67th minute with a header that bounced off Williamson, who had a night to forget, and into the net.
The Lionesses pressed but could not find a way past a solid Australian defence, as they lost for the first time under Wiegman's tenure.
Australia play France in a friendly on July 14, before their World Cup opener against Ireland six days later. England kick off their World Cup campaign against Group D opponents Haiti on July 22.
