Around 1259 he married Anastasia (c. 1245 – 15 March 1317), the daughter of Duke Barnim I of Pomerania.

This pilgrimage is considered a Crusade according to Thomas Fuller in his Historie of the Holy Warre.

Along the way, Henry was taken prisoner and deported to Cairo, where he was held in captivity by the Mamluks for 27 years.

In 1299, he formally resumed his reign, although he probably left the business of government mostly to his son Henry II.

Henry I died in 1302 and was buried in the ducal crypt in the Doberan Minster.