During World War I, Leni started directing as well with films such as Der Feldarzt (Das Tagebuch des Dr. Hart, 1917), Patience (1920), Die Verschwörung zu Genua (1920/21) and Backstairs (1921).

Leni designed short prologues for festive film premieres in Berlin cinemas, such as Lubitsch's Forbidden Paradise (1924), Herbert Brenon's Peter Pan (1924), and E. A. Dupont's Variety (1925).

There Leni made a distinguished directorial debut with The Cat and the Canary (1927), an adaptation of John Willard's stage play.

The film had a great influence over Universal's later classic "haunted house" horror series, and was subsequently remade several times, notably in 1939 with Bob Hope.

The following year he directed the big budget The Man Who Laughs (based on the novel by Victor Hugo), one of the most visually stylized of late period silent films.