John IV was the only son of the Duke Magnus I of Mecklenburg and his wife Elisabeth of Pommern-Wolgast.

Ernst Boll incorrectly refers to him as "John III" in his History of Mecklenburg, Part 1.

He helped his uncle Albert III in the enforcement of the latter's rights as Swedish king.

The Germans had 900 infantry, their leader was called Enis, a German and a relative of Albert; another leader was called "Maekingborg", also a relative of Albert.

[2] John married twice: first to Countess Jutta of Hoya, who died in 1415, and secondly, in 1416, to Catherine, daughter of Duke Eric IV of Saxe-Lauenburg.