Thomas was born into the gens (clan) Nánabeszter, which possessed landholdings along the river Danube in Central Hungary, in the surrounding area of royal capitals Esztergom and Buda.
He inherited Michael's landholdings in Berki, Érd, Sóskút and Tárnok (Deszka), which lay in Pest and Fejér counties along the right bank of the river Danube.
[6] In June 1278, Thomas and his brother Lawrence managed to obtain further territories in Érd, namely the then uninhabited land of royal armor-bearers, which they were granted by King Ladislaus IV.
[2] By the 1280s, Thomas became a prestigious landlord in the region, who endeavored to form his estates into single coherent areas in Central Hungary, southwest of the capital Buda – continuing the late Michael's political orientation.
His local influence and wealth are well illustrated by a letter from Archbishop Lodomer, who requested him to take Michael, the abbot of Csanád (today Cenad, Romania) under his patronage.
King Charles I endowed the majority of his property – portions in Berki, Sóskút, Érd (two), Tárnok, Ében (two), Keszi and Sasad (which laid at the foot of the hill Sashegy, today a borough of Újbuda, the 11th district of Budapest) – to his influential confidant Thomas Szécsényi in 1323.