His book De Republica emendanda (O poprawie Rzeczypospolitej) was widely read and praised across most of Renaissance Europe, influencing thinkers such as Jean Bodin, Hugo Grotius and Johannes Althusius.

Modrzewski family belonged to the gentry (though some authors speak of impoverished nobility), bore Jastrzębiec coat of arms, and held the hereditary title of mayor (wójt/vogt/advocatus) of Wolbórz.

Having lived for a time in Germany, where he studied at the Lutheran University he met Martin Luther and other early Protestant reformers in Wittenberg.

Since he was leaning strongly towards the reformist circles (especially Calvinian and Arian/Polish brethren), he became in danger of being accused of heresy and was ultimately stripped of his ecclesiastical titles and offices.

Modrzewski debuted as a writer in 1543 with the work called Lascius, sive de poena homicidii (On The Penalty for Manslaughter; or Łaski, czyli O karze za mężobójstwo in Polish).

He wrote that peasants should own the soil which they work, and that townsfolk should be able to buy land and be elected to offices (those rights were being reserved only for the nobility back then), demanded the reform (secularization) of education, and division between state and church.

The first complete edition – consisting of all five beforementioned books, and dialogues entitled: De utraque specie Coenae Domini ('On the twofold nature of the Lord's Table') – was published in 1554 in Basel by Johannes Oporinus, after which Modrzewski was forced to leave the capital.