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

Return flights

10 Sep - 17 Sep	Air Canada
10 Sep - 18 Sep	Air Canada
23 Sep - 07 Oct	Air Canada
15 Sep - 22 Sep	Air Canada
24 Sep - 01 Oct	WestJet
14 Sep - 30 Sep	Icelandair
17 Sep - 20 Sep	Air Canada
24 Sep - 26 Sep	WestJet
17 Sep - 23 Sep	Icelandair
23 Sep - 30 Sep	Icelandair
24 Sep - 30 Sep	Lufthansa
26 Sep - 18 Oct	Scandinavian Airlines
14 Sep - 04 Oct	Icelandair
25 Sep - 08 Oct	Icelandair
15 Sep - 29 Sep	Air Canada
21 Sep - 11 Oct	Icelandair
28 Sep - 18 Oct	WestJet
25 Sep - 18 Oct	Turkish Airlines
24 Sep - 12 Oct	WestJet
18 Sep - 11 Oct	Turkish Airlines

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

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 September from $504

Return flights