After 1917 he worked as a Soviet diplomat, a year later he was interned as a hostage in exchange for a British SIS agent Robert Bruce Lockhart, arrested in Moscow (August 31, 1918). In 1921 Enoch Meyer Wallach-Finkelstein was appointed First Deputy People's Commissar of Foreign Affairs.
In 1930 he assumed the leadership of the People's Commissariat for Foreign Affairs, after a conflict with his then-superior, Georgy Chicherin. He supported the idea of the agreement with France and the United Kingdom. He was instrumental in signing the peace treaties with USSR's neighboring countries (the Litvinov Protocol, the Soviet-Polish Non-Aggression Pact of 1932), the restoration of diplomatic relations with the United States in 1933, and the accession of the Soviet Union to the League of Nations in 1934.
He managed to divert the attention of the rest of the world from the crimes committed in USSR (collectivization, the Great Purge or the Great Terror) by proclaiming the slogans of disarmament and the fight against fascism, which led to the rise of authority and prestige of the Soviet authorities. He introduced into diplomacy the term "peaceful coexistence" and the phrase "peace is indivisible".
On May 3rd 1939, he was removed from his post by Joseph Stalin, when the Soviet leader decided to strengthen the cooperation with Reich's dictator Adolf Hitler. After his dismissal, all of his associates were arrested.
Between the years 1941-43 he served as the USSR's Ambassador to the United States, and, since 1942, also to Cuba. Upon his return to Moscow, he assumed the position of the deputy of People's Commissar of Foreign Affairs, and continued working there until 1946. A member of the Central Committee of the Communist Party of the Soviet Union since 1934, removed from the it in 1941.