Jan Gruszczyński was a medieval Bishop of Kraków, Kujawski,[1] Archbishop of Gniezno, Chancellor of the Crown, and active diplomat.

[2] He was born at Sieradz, Central Poland in 1405 AD into the Poraj Polish noble family.

He was the son of John Sieradzki, a military officer of Gruszczyce, and his wife Margaret of Naramowice.

In 1440, he travelled with King Władysław III of Varna to Hungary and then two years later took up in the rectory in his home town of Sieradz.

Although he took ill in 1469 he managed a number of other missions but he died suddenly in Kraków on 8th or 9 October 1473 and was buried in Gniezno Cathedral, where his successor John devoted a magnificent tombstone of red marble.