Shimazu Tadanaga served as a retainer of the Satsuma domain in the early Edo period.  He served as the head of the Nagayoshi-Shimazu family.

In 1592, Tadanaga was born as the lineal heir of Kiire Tadatsugu. 

In 1600, at the Battle of Sekigahara, Shimazu Toyohisa was killed in action and had no heir.  In 1604, Shimazu Tadanao, the younger brother of Toyohisa, was ordered to succeed him, but declined on account of frail health.  As a result, Tadanaga, as the brother-in-law of Tadanao, Tadanaga was treated as the adoptee of Toyohisa and inherited the Nagayoshi-Shimazu family.

In 1624, Tadanaga died at the age of twenty-eight.  He was succeeded by Shimazu Iehisa‘s ninth son, Hisataka, as an adoptee.

Tadanaga’s wife followed him, dying on 2/26, just nine days after Tadanaga.  She was twenty-eight years old.