A 1921 portrait by Matisse found in the private collection of the reclusive Cornelius Gurlitt was looted by the Nazis from a prominent French art collector and should be returned to his heirs, a team of international experts said on Wednesday.

The painting, “Seated Woman/Woman Sitting in Armchair,” depicting a subject in a flowered blouse with a blue fan in her lap, is the first picture from Mr. Gurlitt’s private collection to have its ownership history clarified. The team’s investigation followed an outcry over German authorities’ initial lack of transparency in handling the works, which have become known as the Munich Art Trove.