Second Polish Republic and the Soviet Union had established tentative diplomatic relations during the Polish–Soviet War (1919–1920) for the purpose of negotiation wartime treaties, but neither state had a stable diplomatic mission in the other country.
Such missions were created in the aftermath of the Peace of Riga negotiations (March 1921).
On 23 July 1923, Poland recognized the creation of the Soviet Union, the representatives for Russian and Ukrainian SSRs were to be replaced by a single representative of the United SSR (USSR).
Soviet Union established official diplomatic relations with its own puppet Polish communist government, the Polish Committee of National Liberation, on 1 August 1944.
On 5 January 1945 an official Soviet embassy was opened to the Provisional Government of the Republic of Poland.