If you are a visitor to Western Australia you may drive on your overseas/interstate licence until it expires. You must carry your licence at all times when driving and comply with any conditions (where reasonable) that are endorsed on the licence.
If you have a permanent residence visa and intend on living in WA you must obtain a WA drivers licence within 3 months of getting the visa. After this period your overseas authority to drive will not be recognised. www.dpi.wa.gov.au
THIS IS NEW LEGISLATION YOU NOW ONLY HAVE 3 MONTHS OF GETTING YOUR VISA, BEFORE YOU HAD 3 MONTHS AFTER ARRIVAL INTO PERTH. MAKE SURE YOU ARE COVERED FOR INSURANCE PURPOSES.