Shigetsuna was the second son of Gamô Sadahide and the adopted son of Aochi Nagatsuna (who resided in the Kurita District of Ômi Province). He submitted to Oda Nobunaga along with his brother Gamô Katahide around 1569. The following year Shigetsuna accompanied the Oda army in a campaign against the Asakura of Echizen. At the time Asai Nagamasa elected to break his alliance with the Oda and come to the aid of the Asakura. The Oda army was forced to retreat and Aochi was killed fighting in the rear guard.