The low was recorded shortly before 7:00am as residents awoke to crisp, clear skies.
The city’s previous coldest morning this year was on June 29, when temperatures fell to 3.8C.
Bureau of Meteorology forecaster Steven McInerney said it was Perth’s coldest morning since August last year.
The city recorded a temperature of 1.7C on August 2, 2017.
Another cold night is expected tonight, the BOM said.
“We’re actually forecasting around about 3C tomorrow morning and then it will begin to slowly increase,” Mr McInerney said.
“Sunday morning we are looking at 5C and then 8C for Monday.”
In addition to the cold snap, the BOM also said Perth was in the middle of its wettest start to August in a long time.
The city had recorded 101.6 millimetres of rain up to 9:00am yesterday morning.
The BOM said it was the wettest first nine days at Mt Lawley on record, dating back to 1993, and the wettest in Perth since 1945, when the city received 103.1mm.