AirHint found the following cheapest return flights from Seattle (SEA) to Sydney (SYD) in December 2025 (see full year).
Return flights
| 15 Dec - 29 Dec | Air Canada | ||
| 31 Dec - 31 Jan | Delta | ||
| 24 Dec - 30 Dec | Air Canada | ||
| 23 Dec - 31 Dec | Air Canada | ||
| 11 Dec - 02 Jan | United | ||
| 14 Dec - 09 Jan | Delta | ||
| 19 Dec - 03 Jan | Air Canada |
Also check the deals for one-way flights from Seattle to Sydney in December.
The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.
Find us on social media