He was born at Kitano in Kasugai District, Owari Province, the son of Yasui Shigetsugu, lord of Miyaushiro Castle. His first name was Nagayoshi, and he took the name Nagamasa only late in life. Later, because his uncle Asano Nagakatsu, an archer in Oda Nobunaga's service, had no son, he was adopted into the Asano house as husband of Nagakatsu's daughter Yaya and succeeded to the family.
Nene, who had become the adopted daughter of his uncle Nagakatsu, married Kinoshita Tōkichirō, the later Toyotomi Hideyoshi. Nagayoshi and Hideyoshi thus became brothers-in-law sharing the same father-in-law, making him one of Hideyoshi's closest relatives. Through this tie he was assigned to Hideyoshi by Nobunaga's order, and thereafter supported his rise.
He distinguished himself in the attack on Odani Castle in Ōmi, defended by Azai Nagamasa. When Hideyoshi became lord of Odani, Nagayoshi too was given lands worth one hundred twenty koku in Ōmi. Though small, this marked the start of his role at the core of Hideyoshi's retainers. Later, at the siege of Miki Castle in Harima, he also took part in surrender talks with its lord Bessho Nagaharu.
After the Honnō-ji Incident he served Hideyoshi and distinguished himself at the Battle of Shizugatake. For this he was given more than twenty thousand koku in Kōka and Ōtsu in Ōmi, becoming a daimyō, and he entered Seta Castle and then Sakamoto Castle. Being entrusted with key points of transport on Lake Biwa showed Hideyoshi's deep trust.
He was appointed magistrate governing Kyoto and later became one of the Five Magistrates of the Toyotomi government. Valued for his excellent administrative skill, he carried out the Taikō land survey in many regions on Hideyoshi's orders. He was also entrusted with managing gold and silver mines confiscated from daimyō, supporting the Toyotomi government more through political and financial ability than through valor.
When Hideyoshi's younger sister Asahi-hime was married to Tokugawa Ieyasu as his principal wife, Nagayoshi escorted her as far as Hamamatsu. It was an important match meant to win Ieyasu over. On Hideyoshi's orders he also abandoned Sakamoto Castle and built a new castle at Ōtsu on the shore of Lake Biwa. He is thought to have moved his base to Ōtsu by the next year.
After serving in the pacification of Kyushu, he was given the whole province of Wakasa, some eighty thousand koku, becoming a daimyō ruling an entire province. The next year he surveyed the land in his domain, and the year after that he carried out a sword hunt. He took the lead in applying Hideyoshi's policies in his own province, setting an example of the new form of rule.
In the Odawara campaign, when Hideyoshi cautiously refused to cross a pontoon bridge built by Ieyasu's retainer, Nagayoshi is said to have crossed first to prove it safe. From the late stage of the campaign and in its aftermath he took the central role in place of Ishida Mitsunari, and in the following Ōshū settlement he was the executor, handling the disposition of northeastern daimyō and the response to uprisings.
Hideyoshi gave Nagayoshi some fifty thousand koku in Kai Province and his son Yoshinaga one hundred sixty thousand, and ordered him to act as intermediary with eastern daimyō such as the Date and Nanbu. This is thought to have been a role meant to hold Tokugawa Ieyasu in the Kantō in check. Nagayoshi himself remained at Hideyoshi's side as magistrate, while Yoshinaga governed Kai.
Accused of involvement in the previous year's Hidetsugu Incident, he and his son Yoshinaga nearly received a severe punishment from Hideyoshi, but missionary reports record that through the mediation of Tokugawa Ieyasu and Maeda Toshiie the matter was reexamined and found to stem from letters forged by a former retainer. In the great Fushimi earthquake that year, he rushed at once to Hideyoshi's side.
Missionary records state that after Hideyoshi's death his rivalry with Ishida Mitsunari deepened. That year he fell under suspicion of plotting to assassinate Tokugawa Ieyasu and was ordered into confinement at Kōfu. Nagamasa handed headship of the family to his son Yoshinaga and retired to Fuchū in Musashi Province, where a site said to be his place of retreat survives.
At the Battle of Sekigahara he joined Ieyasu's Eastern Army and served as keeper of Edo Castle in Ieyasu's absence. That a magistrate once at the heart of the Toyotomi government stood with Ieyasu showed the direction of the times. His son Yoshinaga distinguished himself in the main battle and rose greatly to become daimyō of some three hundred seventy thousand koku at Wakayama in Kii.
Recognized for his service at Sekigahara, he was given fifty thousand koku at Makabe in Hitachi Province and became the first lord of the Makabe domain. He had moved to Edo the year before, and after the Edo shogunate was founded he served close to Ieyasu. Adapting to the changing times, he kept his house alive, moving from senior Toyotomi retainer to daimyō serving the Tokugawa.
He died at his residence in Makabe, Hitachi Province. His remains were placed at Shitchi-in on Mount Kōya, and the Makabe domain of fifty thousand koku passed to his fourth son Nagashige. His was a life that supported the politics and finances of the Toyotomi government as Hideyoshi's brother-in-law and in the end preserved his house in the Tokugawa age. His descendants became lords of the Hiroshima domain, and the Asano house continued throughout the Edo period.
Oda NobunagaToyotomi HideyoshiMaeda ToshiieTokugawa IeyasuAzai NagamasaIshida Mitsunari
Takeda KatsuyoriMogami YoshiakiOichiSanada MasayukiSatake YoshishigeOda Nagamasu (Urakusai)Honda TadakatsuNene (Kōdai-in)
People of the Sengoku/Azuchi-Momoyama period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.