John Albert was born in Güstrow, the eldest son of the Duke Albrecht VII of Mecklenburg-Güstrow and his wife Anne of Brandenburg.

When his father died in 1547, John Albert and his brothers Ulrich III and George were jointly invested with the Duchy of Mecklenburg-Güstrow by Emperor Charles V. Initially, John Albert administered the Mecklenburg-Güstrow part of the Duchy alone, while Ulrich administered the Bishopric of Schwerin from 1550 as successor to his cousin Magnus III and George fought in the Schmalkaldic War and fell in 1552 before Frankfurt am Main.

As a convinced adherent of Protestantism John Albert I, unlike his father, decided to back the introduction the Reformation in his lands.

In February 1550, he concluded a defensive alliance with Margrave John of Brandenburg-Küstrin and Duke Albert of Prussia, to whose daughter, Anna Sophia, he was engaged and later married.

Duke John Albert was considered a modern Renaissance prince and a patron of the arts and sciences, with an open mind for the scientific discoveries of his time.

They jointly visited the imperial court in Vienna, where they studied architecture and modern fortification techniques, which they subsequently applied in Mecklenburg.