AirHint found the following cheapest return flights from Seattle (SEA) to Lisbon (LIS) in August 2025 (see full year).

Return flights

20 Aug - 24 Aug	Icelandair
09 Aug - 24 Aug	Icelandair
20 Aug - 28 Aug	Icelandair
30 Aug - 04 Sep	Icelandair
20 Aug - 26 Aug	United
11 Aug - 20 Aug	Icelandair
17 Aug - 24 Aug	Icelandair
12 Aug - 20 Aug	Air France
15 Aug - 22 Aug	Icelandair

Also check the deals for one-way flights from Seattle to Lisbon in August.

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 Lisbon in August from 445€

Return flights