Raczkiewicz, who was already in Paris, immediately took his constitutional oath at the Polish Embassy and became President of the Republic of Poland. He then appointed General Władysław Sikorski to be Prime Minister and Commander-in-Chief of the Polish Armed Forces.
Most of the Polish Navy escaped to Britain, and tens of thousands of Polish soldiers and airmen escaped through Hungary and Romania or across the Baltic Sea to continue the fight in France. Many Poles subsequently took part in Allied operations in Norway (Narvik), France, the Battle of Britain, the Battle of the Atlantic, North Africa (notably Tobruk), Italy (notably at Cassino and Ancona), Arnhem, Wilhelmshaven and elsewhere beside other Allied forces. Even after the fall of Poland, and before the Soviet Union's entry into the war, Poland remained the third strongest Allied belligerent, after France and Britain. (Other Polish military units, formed in the Soviet Union after Hitler's invasion of the Soviet Union in June 1941, fought alongside and under the command of the Soviets.)
When Germany attacked the Soviet Union in 1941, the Polish Government in Exile established diplomatic relations with the Soviet Union, despite Stalin's role in the earlier dismemberment of Poland. Hundreds of thousands of Polish soldiers who had been taken prisoner by the Soviets in eastern Poland in 1939, and many civilian Polish prisoners and deportees, were released and allowed to form military units ("Anders' Army"); they were evacuated to Iran and the Middle East, where they were desperately needed by the British, hard pressed by Rommel's Afrika Korps. These Polish units formed the basis for the Polish 2nd Corps, led by General Władysław Anders, which together with other, earlier-created Polish units fought alongside the Allies.
In April 1943 the Germans announced that they had discovered at Katyn Wood, near Smolensk, Russia, mass graves of 4,300 Polish officers who had been taken prisoner in 1939 and murdered by the Soviets. The Germans invited the International Red Cross to visit the site, and the graves were confirmed to contain the corpses of Polish officers who had been killed with Soviet weapons. The Soviet government said that the Germans had fabricated the discovery. The other Allied governments, for diplomatic reasons, formally accepted this; the Polish Government in Exile refused to do so.
Stalin then severed relations with the Polish Government in Exile. Since it was clear that it would be the Soviet Union, not the western Allies, who would liberate Poland from the Germans, this breach had fateful consequences for Poland. In an unfortunate coincidence, Sikorski, widely regarded as the most capable of the Polish exile leaders, was killed in an air crash at Gibraltar in July 1943. He was succeeded as head of the Polish Government in Exile by Stanisław Mikołajczyk.
During 1943 and 1944 the Allied leaders, particularly Winston Churchill, tried to bring about a resumption of talks between Stalin and the Polish Government in Exile. But these efforts broke down over several matters. One was the Katyń massacre (and others at Kalinin and Kharkiv). Another was Poland's postwar borders. Stalin insisted that the territories annexed by the Soviets in 1939, which had millions of Poles in addition to Ukrainian and Belarusian populations, should remain in Soviet hands, and that Poland should be compensated with lands to be annexed from Germany. Mikołajczyk, however, refused to compromise on the question of Poland's sovereignty over her prewar eastern territories. A third matter was Mikołajczyk's insistence that Stalin not set up a Communist government in postwar Poland.
In November 1944, despite his mistrust of the Soviets, Mikołajczyk resigned to return to Poland and take office in the new government established under the auspices of the Soviet occupation authorities. Many Polish exiles opposed this action, believing that this government was a façade for the establishment of Communist rule in Poland, a view that was later proven correct; after losing an election which was later shown to have been fraudulent, Mikołajczyk left Poland again in 1947.
Meanwhile the Polish Government in Exile had maintained its existence, but the United States and the United Kingdom withdrew their recognition on July 6, 1945. The Polish Armed Forces in exile were disbanded in 1945, and most of their members, unable to safely return to Communist Poland, settled in other countries. The London Poles had to vacate the Polish embassy on Portland Place and were left only with the president's private residence at 43 Eaton Place. The Government in Exile became largely symbolic of continued resistance to foreign occupation of Poland, while retaining some important archives from prewar Poland. The Republic of Ireland, Spain and the Vatican City (until 1979) were the last countries to recognize the Government in Exile, though the Vatican — through Secretary of State Domenico Tardini — had withdrawn diplomatic privileges from the envoy of the Polish pre-war government in 1959.
In 1954, political differences led to a split in the ranks of the Government in Exile. One group, claiming to represent 80% of 500,000 anti-Communist Poles exiled since the war, was opposed to President August Zaleski's continuation in office when his seven-year term expired. It formed a Council of National Unity in July 1954, and set up a Council of Three to exercise the functions of head of state, comprising Tomasz Arciszewski, General Władysław Anders, and Edward Raczyński. Only after Zaleski's death in 1972 did the two factions reunite.
Some supporters of the Government in Exile eventually returned to Poland, such as Prime Minister Hugon Hanke in 1955 and his predecessor Stanisław Mackiewicz in 1956. The Soviet installed government in Warsaw actively campaigned for the return of the exiles, promising decent and dignified employment and forgiveness of past transgressions.
Despite these setbacks, the Government in Exile continued in existence. When Soviet rule over Poland came to an end in 1989, there was still a president and a cabinet of eight meeting every two weeks in London, commanding the loyalty of many of about 150,000 Polish veterans and their descendants living in Britain, including 35,000 in London alone.
In December 1990, when Lech Wałęsa became the first post-Communist president of Poland, he received the symbols of the Polish Republic (the red presidential banner, the presidential and state seals, the presidential sashes, and the original text of the 1935 Constitution) from the last president of the Government in Exile, Ryszard Kaczorowski, thus re-establishing the continuity of the Republic and in effect retroactively recognizing the legitimacy of the Government in Exile. In 1992, military medals and other decorations awarded by the Government in Exile were officially recognized in Poland.