Tomasz became Colonel of the Crown Army in 1765, Chamberlain of King Stanisław II Augustus in 1767, castellan of Czersk since 1777, Court Treasurer since 1791, Marshal of the Sejm of the Duchy of Warsaw in 1809 and later President of the Senate of the Duchy of Warsaw and the Kingdom of Poland.

He was the founder of Tomaszów Mazowiecki[2] Son of Piotr Ostrowski and Konstancja Stoińska.

After the death of Józefa in 1780 he married Apolonia Ledóchowska (in 1781), with whom he had nine children most notably Antoni Jan Ostrowski, General Commander of the National Guard during the November Uprising and Władysław Ostrowski, Marshal of the Sejm of the Polish Kingdom in 1830.

A true hero of the country, he restrained the king from accession to the Targowica Confederation and he was subsequently imprisoned by the Russians.

During the Polish-Russian war, at the meeting of 23 July 1792 he strongly opposed the decision of King Stanisław II Augustus on his accession to the Confederation of Targowica and he enhanced to revolt against the Russians and the administration which had control over the Polish–Lithuanian Commonwealth.