He was born in Mirow to Duke Charles Louis Frederick of Mecklenburg and his wife Princess Elisabeth Albertine of Saxe-Hildburghausen.

His father was the second son of Adolphus Frederick II, Duke of Mecklenburg.

[1] He was the heir presumptive of Mecklenburg-Strelitz from the death of his father on 5 June 1752 until he succeeded his uncle Duke Adolphus Frederick III on 11 December 1752.

They were additionally under the protection of King George II of Great Britain.

In 1761, his sister Charlotte married King George III of Great Britain.