AirHint found the following cheapest return flights from Seattle (SEA) to London (STN) in December 2025 (see full year).

Return flights

01 Dec - 11 Dec	Icelandair
04 Dec - 07 Dec	Icelandair
01 Dec - 07 Dec	Icelandair
12 Dec - 15 Dec	Icelandair
12 Dec - 28 Dec	Icelandair
12 Dec - 30 Dec	Icelandair
12 Dec - 29 Dec	Icelandair
22 Dec - 27 Dec	Icelandair
08 Dec - 30 Dec	Aer Lingus
02 Dec - 07 Dec	Alaska Airlines
12 Dec - 04 Jan	Air Canada
26 Dec - 09 Jan	Icelandair
12 Dec - 03 Jan	Air Canada
23 Dec - 02 Jan	Air Canada
26 Dec - 02 Jan	Air Canada
13 Dec - 03 Jan	Icelandair
19 Dec - 04 Jan	Icelandair
17 Dec - 02 Jan	Icelandair
19 Dec - 10 Jan	Aer Lingus
19 Dec - 02 Jan	Aer Lingus

Also check the deals for one-way flights from Seattle to London 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.

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Cheapest return flights from Seattle to London in December from $527

Return flights