He was the oldest son of common land owners, Felicjan and Brygida née Szczakowska, and grew up under the protection of his uncle, Wacław Szczakowski.

After his return to Prussia, he started his ecclesiastical career by serving as a canon in the Prussian communities of Wiślica (Wislitz) and Włocławek.

Prussian authorities, considering Dunin's loyalty to the King of Prussia, recommended him as a candidate for the sees of archbishops of Poznań and Gniezno.

As proof of his loyalty and on demand of the president of Grand Duchy of Posen, Eduard Flottwell, Dunin wrote a pastoral letter condemning the November Uprising.

After his return to Poznań, Dunin swore loyalty to the new king, but he continued his anti-Prussian politics in church until his death.