His first assignment as an intelligence officer was to assist in increasing sugar production in the Dominican Republic by working out property and contractual conflicts among rural landowners.

Immediately after World War I, Berle became a member of the American delegation to the Paris Peace Conference, advocating for smaller nations' rights of self-determination.

[5] While some advocated trust busting, breaking up the concentrations of firms into smaller entities to restore competitive forces, Berle believed that that would be economically inefficient.

"[7] Berle was an original member of Franklin D. Roosevelt's "Brain Trust", a group of advisers who developed policy recommendations.

'"[11] by 1941, Berle had charge of the intelligence activities in the State Department, working with the FBI in Latin America and the OSS in Europe.

Critics on the left accused him of being too hostile toward Moscow, and Secretary of State Cordell Hull was annoyed at his access to Roosevelt.

The other, led by Osmond Fraenkel and Thomas I. Emerson, supported freedom of speech and press as well as Anti-Fascism (seen at the time as a Popular Front stance, thus pro-Communist).

During the NLG's 1940 convention, newly elected president Robert W. Kenny of California and secretary Martin Popper of New York sought to persuade members to return.

[citation needed] Explaining Berle's evasive testimony, Allen Weinstein wrote in his book Perjury: The Hiss-Chambers Case: "His major concern in 1948, at a time when Berle was a Liberal Party leader in New York working for Truman's election, was to defuse, if possible, the influence of anti-Communist sentiment and of the case itself in that election year.

Berle also was a major architect in the development of federal farm and home owners' mortgage programs and in the expansion of the Reconstruction Finance Corporation.

In October 1945, two days after the deposition of president Getúlio Vargas, Berle pledged for the freedom of the Brazilian communists who were being incarcerated by the government since the beginning of the month.

Berle briefly returned to government service for the first half of 1961, serving under President John F. Kennedy as head of an interdepartmental task force on Latin American affairs.

During that time, he was primarily involved in forming the US response to a newly communist Cuba, which included both the failed Bay of Pigs invasion and the initiation of the Alliance for Progress, an economic development policy aimed at the region.

His article on "Property, Production and Revolution" was a key statement of the theory behind the Great Society program of President Lyndon B. Johnson.