Born in 1530 at Kasugayama Castle as the fourth son of Nagao Tamekage, deputy shugo of Echigo. Known in childhood as Torachiyo, he entered Rinsenji Temple at seven, studying Zen and the classics under Tenshitsu Koiku. Succeeding his elder brother Harukage at nineteen, he unified Echigo Province. In 1561 he received the Uesugi surname and the office of Kanto Kanrei from Uesugi Norimasa, thereafter bearing the names Masatora, Terutora, and finally Kenshin. He fought Takeda Shingen in five battles of Kawanakajima, the fourth of which (1561) gave rise to the legend of their single combat. Undaunted by the Hojo and Takeda, he repeatedly campaigned into the Kanto and Hokuriku regions. Renowned for his devotion to righteousness, he famously sent salt to his enemy Takeda when the Hojo cut off supplies. He took a vow of lifelong celibacy and worshipped Bishamonten fervently, flying the single-character 'Bi' banner. He collapsed at Kasugayama Castle on the 13th day of the third month of 1578 and died suddenly at forty-nine, likely of a stroke. His death poem — 'Forty-nine years, a single dream; a lifetime of glory, a single cup of sake' — survives as the crystallization of the War God's life.

Renowned for his deep devotion to righteousness — helping the weak and refusing to bow to the strong. Deeply devoted to Zen and Bishamonten, he remained unmarried throughout his life. He loved sake and showed almost divine judgment on the battlefield, yet lived personally in simplicity.

Celebrated as "The God of War" and "The Dragon of Echigo," he stands among the greatest generals of the Sengoku era. His duels with Takeda Shingen at Kawanakajima and his code of righteousness profoundly shaped Japanese ideals of bushido. The ruins of Kasugayama Castle and Rinsenji Temple in Joetsu, Niigata remain sacred sites for history enthusiasts.