He was Count of Wied-Neuwied from September 17, 1737 to May 29, 1784, when he was elevated to Prince and continued to rule in that capacity until his death on August 8, 1791. They had three children Frederich Karl of Wied, who succeeded him as Prince, Alexander August of Wied and Sophie Karoline of Wied. In 1737, after his studies in Strasbourg and Königsberg, he was instrumental in the negotiation of the Vienna peace, which ended the War of the Polish Succession.
When the title of prince was offered to him in 1738, however, he declined for financial reasons.
During his reign he sought to advance, socially and economically, the small territory of Wied-Neuwied. His governance was characterised by openness and religious tolerance.
Foreign this reason, historian Max Braubach has described him as "one of the best representatives of enlightened absolutism in the realm."
As Chairman of the Lower Rhenish-Westphalian Count College, Johann Friedrich Alexander was able to play a role in national politics.