The Icelandic budget carrier made the announcement just hours after stating it was in the “final stages” of securing fresh investment.
Passengers have been advised to make alternative travel plans.
MORE: WOW Air cancels all flights as financial woes worsen
"WOW Air has ceased operation. All WOW Air flights have been cancelled," said the airline in a statement.
"Passengers are advised to check available flights with other airlines.
"Some airlines may offer flights at a reduced rate, so-called rescue fares, in light of the circumstances.
"Information on those airlines will be published when it becomes available."
Passengers who paid with credit cards are advised to contact their card issuer for refunds.
Anyone whose flights are part of a package should contact their travel agent for assistance under the Atol scheme.
Those who have bought additional protection, or have protection through their credit card issuer, may be able to claim compensation and assistance for delays and disruption.
Further information will be made available via the WOW Air website.
The CAA has issued guidance to passengers on account of WOW’s operations at Gatwick, Stansted and Ebinburgh.
It says customers who booked directly with WOW and paid by credit card may be protected under Section 75 of the Consumer Credit Act 1974 and should contact their card issuer.
"Similarly, if you paid by debit or charge card you should contact your card issuer for advice as you may be able to make a claim under their charge back rules.
"If you purchased travel insurance that may include cover for scheduled airline failure, known as SAFI, you should contact your insurer. If you did not book directly with WOW Air and purchased your tickets through an intermediary, you should contact your booking or travel agent in the first instance."
