As he was only eighteen when his father died, a regency ruling Mecklenburg-Schwerin for him for the next nine years. On 17 February 1588 he married Sophie of Holstein-Gottorp and they became the parents of three children. 
When, in 1585, he was handed over the ruling of his territories, he was confronted with problems. Debts and other pressures became almost too much for him. One of his greatest pressures was his uncle, Christoph, constantly demanding a bigger part of his country. In 1590, sick and tired of these problems, he wanted to quit governing and leave the country. On 22 March 1592, after an argument with his uncle, he committed suicide. 
According to religious laws, suicide was a deadly sin and would have prevented him from being buried in religious grounds. Courtiers then decided he had been murdered by the devil in a pact with two women from Schwerin. Katharina Wankelmuth died in the torture chamber and Magdalena Rukitz was burned at the stakes. The thirty-four year old Duke Johann was then buried in the "Heilige Blutskapelle" in the Cathedral of Schwerin. 
His wife, having married him when she was nineteen, at twenty-three was a widow. As their sons were only four and two years old, the government was handled by officials who were only interested in their own advancement. 

Source: Leo van de Pas