Born a son of Azai Hisamasa, lord of northern Ōmi (Shiga). The Azai were then subordinate to the Rokkaku of southern Ōmi, and Nagamasa is said to have been born in the Rokkaku castle town.
At 15 he defeated the great Rokkaku army at Norada. He divorced his wife, daughter of a Rokkaku retainer, signaling independence, and the retainers made the young Nagamasa head of the house.
He married Oichi, Oda Nobunaga's sister, and allied with Nobunaga (year debated). They had three daughters, Chacha, Hatsu and Gō, and are said to have been a loving couple.
When Nobunaga escorted Ashikaga Yoshiaki to Kyoto, Nagamasa helped him attack the Rokkaku.
When Nobunaga attacked the Asakura of Echizen, longtime friends of the Azai, Nagamasa turned on him and struck from behind; Nobunaga barely escaped from Kanegasaki. Retainers valuing the old Asakura ties reportedly pressed for this.
With the Asakura he fought the Oda-Tokugawa army at the Anegawa and lost, but continued resisting Nobunaga in league with Hongan-ji, the Takeda and others.
After the Asakura were destroyed, Nobunaga besieged his seat at Odani castle. Sending his wife Oichi and three daughters out to Nobunaga, he took his own life, at 28.
Oda NobunagaAshikaga YoshiakiAsakura YoshikageToyotomi HideyoshiAsano NagamasaTōdō TakatoraYodo-donoTokugawa Hidetada
Tokugawa IeyasuKanō EitokuFuruta OribeTakenaka Shigeharu (Hanbei)Kuroda Yoshitaka (Kanbei)Takeda KatsuyoriMogami YoshiakiOichi
People of the Sengoku/Azuchi-Momoyama period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.