The history of Łaszczów dates back to 1549, when King Sigismund II Augustus allowed Podkomorzy of Bełz and Castellan of Horodło Aleksander Łaszcz to change his own village of Domaniz into a town of Prawda (named after Prawdzic coat of arms).

Łaszczów was a regional trade and business center, but its prosperity ended after Swedish invasion of Poland (1655–1660).

In 1702, the town was burnt by Swedes, during the Great Northern War, and in 1745, Józef Łaszcz, owner of Łaszczów, initiated construction of a church and Jesuit collegium.

After the Polish victory in the Austro-Polish War of 1809 it was regained by Poles and included within the short-lived Duchy of Warsaw.

Town rights were revoked by the Tsarist administration in 1870 as part of anti-Polish repressions following the unsuccessful Polish January Uprising.