During the German invasion of Poland, which started World War II, on September 13, 1939, Leżajsk was captured by the Wehrmacht. Afterwards, the German "Einsatzgruppe I" entered the town to commit various atrocities against the population. On November 3, 1939, the German security police carried out mass arrests of local Poles as part of the "Intelligenzaktion". The Poles were then either imprisoned in the local prison or massacred at the local cemetery. Among the massacred Poles were teachers, school principals, priests and military officers. Poles from Leżajsk were also among the victims of the large Katyn massacre, committed by the Russians in April–May 1940. During the German occupation, the Home Army was very active in the area. Since May 1940, underground Polish newspaper "Odwet" was distributed in Leżajsk by the Polish resistance movement. On May 28, 1943, Germans shot 43 residents of the town. Leżajsk was captured by the Home Army on July 27, 1944.