He returned to Russia in 1903, and after the 1905 Revolution he became editor of the SDLP's first legal newspaper, Novaya Zhizn (New Life).

When the Russian government began arresting Bolsheviks in 1906, Litvinov left the country and spent the next ten years living in London, where he was active in the International Socialist Bureau. Here he met and married the impulsive, free-spirited Ivy Low.

After the October Revolution, Litvinov was appointed by Vladmir Lenin as the Soviet Government's representative in Britain. However, in 1918, Litvinov was arrested by the British Government and held until exchanged for Bruce Lockhart, a British diplomat who had been imprisoned in Russia.

Litvinov was then employed as the Soviet Government's roaming ambassador. It was largely through his efforts that Britain agreed to end its economic blockade of the Soviet Union. Litvinov also negotiated several trade agreements with European countries.

In 1930, Joseph Stalin appointed Litvinov as Commissar of Foreign Affairs. A firm believer in collective security, Litvinov worked very hard to form a closer relationship with France and Britain. In 1933 he successfully persuaded the United States to officially recognize the Soviet Government. Franklin D. Roosevelt sent comedian Harpo Marx to the Soviet Union as a good-will amabassador, and Litvinov and Marx became friends and even performed a routine on stage together.

Litvinov's Jewish origins created problems for Stalin during his negotations with Germany in 1939 and he was replaced by Vyacheslav Molotov just before the signing of the Nazi-Soviet Pact.

After the outbreak of war with Germany, Joseph Stalin appointed Litvinov as Deputy Commisar of Foreign Affairs. He also served as Ambassador to the United States from 1941 to 1943.