Joachim was the 4th surviving son of Count Karl I of Hohenzollern (1516–1576) from his marriage to Anna (1512–1579), the daughter of Ernst, Margrave of Baden-Durlach.
As the younger son, he was destined for a career in the clergy, typically as a canon.
In order to avoid this, Joachim converted to the Lutheran faith.
He broke away from the Catholic relatives and moved to the Protestant court of the Elector of Brandenburg in Berlin.
On 6 July 1578 in Lohra, he married Anna (d. 1620), the daughter of Count Volkmar Wolf of Hohnstein.