Traditionally said to have been born around 1493, though his exact birth year is uncertain, Irobe Katsunaga was head of the Irobe clan, local lords based at Hirabayashi in Echigo's Iwafune district (present-day Murakami City, Niigata), and served Uesugi Kenshin as a prominent member of the Agakita warrior coalition. At the Fourth Battle of Kawanakajima in 1561, he fought fiercely for the Uesugi cause, rescuing the imperiled unit of Kakizaki Kageie, and for this feat is said to have received, alongside Yasuda Nagahide, a "blood-stained commendation" — a letter of commendation reputedly written in haste on the battlefield — from Kenshin himself. In 1569, during the Honjo Shigenaga Rebellion, when the senior retainer Honjo Shigenaga rose against Kenshin, Katsunaga joined the Uesugi forces besieging Shigenaga's stronghold, Honjo Castle (later Murakami Castle), but is said to have been killed in a night raid by Shigenaga's men (some accounts suggest death by illness instead). The ruins of Hirabayashi Castle are today a National Historic Site.

As his valor at Kawanakajima shows, he was a warrior who combined fierce courage with a strong sense of duty, never abandoning allies in crisis.

The tale of the "blood-stained commendation" that symbolizes the martial reputation of the Irobe clan is still recounted today as an episode illustrating the loyalty and bravery of Uesugi's retainer band. The ruins of Hirabayashi Castle, with its well-preserved main and second enclosures and moats, are maintained as a National Historic Site conveying the castle structure of the Agakita region's local lords.