Do I need a return flight when leaving Australia for over 3 months?

When traveling from Australia for more than three months, whether you need a return flight can depend on various factors, including the type of visa you hold. Generally, those applying for a tourist or visa-exempt category may not need a return ticket, but airlines may enforce their own rules requiring a return ticket for boarding. If you have an exemption that allows you to stay longer, a one-way ticket may be acceptable, as confirmed by a commenter who plans to travel to Thailand for a year.