After the end of the First World War, Lazzari joined the Italian Futurist movement and exhibited with such artists as Giacomo Balla and Gino Severini.
During the era of the Great Depression Lazzari became an American citizen and did commissions for the Works Progress Administration and the Federal Art Project including murals and sculptures.
In the early 1940s, Pietro Lazzari moved permanently to Washington D.C., where he established his studio and participated in the World War II National Artists for Victory exhibition at the Metropolitan Museum of Art (1942).
During the following years Lazzari was awarded a Fulbright Fellowship and received commissions for bronze portraits of Pope Paul VI and Eleanor Roosevelt.
His work includes a pair of murals in the Jasper, Florida post office, commissioned by the Treasury Section of Fine Arts, and completed in 1942.