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

Return flights

05 Sep - 12 Sep	Icelandair
29 Sep - 06 Oct	Icelandair
20 Sep - 27 Sep	Icelandair
02 Sep - 09 Sep	Aer Lingus
09 Sep - 16 Sep	Aer Lingus
08 Sep - 16 Sep	Aer Lingus
06 Sep - 13 Sep	Icelandair
16 Sep - 23 Sep	Aer Lingus
04 Sep - 11 Sep	Icelandair
30 Sep - 07 Oct	Aer Lingus
03 Sep - 10 Sep	Aer Lingus
23 Sep - 07 Oct	Aer Lingus
07 Sep - 14 Sep	Aer Lingus
23 Sep - 01 Oct	Hawaiian Airlines
27 Sep - 04 Oct	Icelandair
27 Sep - 05 Oct	Icelandair
24 Sep - 01 Oct	Turkish Airlines
25 Sep - 02 Oct	Turkish Airlines
25 Sep - 09 Oct	Turkish Airlines
22 Sep - 01 Oct	Turkish Airlines

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

Book a cheap hotel in Lisbon

Cheap car rent in Lisbon

Cheapest return flights from Seattle to Lisbon in September from 500€

Return flights