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

Return flights

02 Sep - 09 Sep	Air Canada
09 Sep - 15 Sep	Air Canada
08 Sep - 15 Sep	Air Canada
19 Sep - 23 Sep	Lufthansa
09 Sep - 13 Sep	Air Canada
04 Sep - 16 Sep	Air Canada
03 Sep - 10 Sep	Lufthansa
03 Sep - 13 Sep	Brussels Airlines
10 Sep - 17 Sep	SWISS
29 Sep - 07 Oct	Air Canada
11 Sep - 17 Sep	Turkish Airlines
18 Sep - 01 Oct	SWISS
25 Sep - 10 Oct	Turkish Airlines
25 Sep - 02 Oct	Turkish Airlines
30 Sep - 05 Oct	TAP	direct
29 Sep - 07 Oct	TAP	direct
19 Sep - 01 Oct	TAP	direct
17 Sep - 14 Oct	Turkish Airlines
28 Sep - 05 Oct	TAP	direct
30 Sep - 07 Oct	TAP	direct

Also check the deals for one-way flights from Washington 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.

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Cheapest return flights from Washington to Lisbon in September from $443

Return flights