When Germany invaded Poland on September 1, 1939, Olechowski was entrusted with the transport of a large part of Poland's gold reserves to the safety of Hungary, then returned to Poland to join the fight against the Germans, and then later against the Soviets.
Olechowski, his wife and daughter were arrested by the Soviet NKVD in January 1940. He was imprisoned at the notorious Lubyanka prison in Moscow, while his wife and daughter were deported to a Soviet gulag. His son remained in Warsaw and participated in activities of the the Polish underground. but was eventually captured by the Gestapo for providing aid to the inhabitants of the Warsaw Ghetto.
He was released but later re-captured during the Warsaw Uprising, and imprisoned at Auschwitz.
Upon Stalin's orders, Olechowski was kept alive because of his expertise in counter espionage but later was transferred to a Soviet gulag. He was released in 1942 as a result of the Sikorski-Mayski agreement and immediately became part of the Second Polish Corps under the command of General Wladysław Anders. He was able to reunite with his wife and daughter and transferred to a Polish refugee camp in Kenya. After World War II he was unable to return to Poland due to a warrant for his arrest by the communist regime.
Olechowski moved to London and then made his way to Canada. He worked tirelessly to publicize information about Soviet war crimes against the Polish people, in particular the Katyn Massacre, which the Soviets adamantly refused to acknowledge. In the Ostrashov incident, largely unknown to the public, the Soviets forced Polish prisoners onto barges which were then sunk in the White Sea.