Ienaga served Tokugawa Ieyasu from a young age, and was famed for his skill with the bow.
He assisted in the suppression of the Ikkō-ikki of Mikawa Province, and this earned him Ieyasu's trust.
After Ieyasu's move to the Kantō region in 1590, Ienaga was granted the 20,000 koku fief of Sanuki in Kazusa Province.
In 1600, he was assigned to Fushimi Castle together with Torii Mototada and Matsudaira Ietada.
Ienaga was succeeded by his son Masanaga, who served during the Osaka Campaign of 1615.