Pető was the son of Márk Gersei but his mother is unknown. The date and place of his birth have not been found.
His wife was Margit Hídvégi. They were married, but the date and place have not been found. Their five known children were János (?-1424), György (?-1396), Tamás (?-<1430), Benedek (?-?) and Dénes (?-?).