He was born in Hazu District, Mikawa, the eldest son of Katō Noriaki, a retainer of Matsudaira Motoyasu, later Tokugawa Ieyasu. In the Mikawa Ikko uprising that broke out that year, his father joined the rebels against Motoyasu, was defeated and driven from the province. The newborn Yoshiaki was taken along by his father as he wandered from place to place.
His father having entered the service of Hashiba Hideyoshi at Nagahama in Ōmi, Yoshiaki, who had been helping peddle horses, was also discovered and became a page to Hideyoshi's adopted son Hidekatsu. He then joined the campaign in Harima without his master's leave and was sharply scolded by Hideyoshi's wife Nene. But Hideyoshi valued his eagerness and made him his direct retainer.
Following Hideyoshi's army, he joined the siege of Miki Castle in Harima for his first battle. In a following fight in Bitchū, still in his mid-teens, he is said to have taken enemy heads for the first time. As one of the warriors raised under Hideyoshi, he rose to prominence alongside Katō Kiyomasa and Fukushima Masanori.
After the Honnō-ji Incident, Hideyoshi fought the Oda senior retainer Shibata Katsuie at Shizugatake. Yoshiaki fought hard with Fukushima Masanori, Katō Kiyomasa and others, winning great distinction and an immediate grant of 3,000 koku. The seven who shone here were called the Seven Spears of Shizugatake, and Yoshiaki was counted among them.
When Hideyoshi became kampaku, Yoshiaki received the court title Samanosuke, and in the Shikoku campaign he joined the conquest of Iyo. For this he was given 15,000 koku on Awaji and became a daimyō. Thereafter he led the Awaji fleet in the Kyushu and Odawara campaigns, distinguishing himself by attacking enemy castles from the sea.
In the Bunroku campaign, Hideyoshi's invasion of Korea, he crossed the sea leading the fleet as second to Kuki Yoshitaka. He fought the Korean navy under Yi Sun-sin many times, and while some allies suffered defeats he drove the enemy off and received a letter of commendation from Hideyoshi. Later he moved to Masaki in Iyo, where he improved rivers and developed the castle town.
In the renewed Keichō campaign he again led the fleet overseas and won great distinction in a sea battle that crushed the Korean navy. But his relations with Tōdō Takatora, a neighbor with whom he competed for merit, grew ever worse. In a debate over withdrawal he alone strongly objected, was praised by Hideyoshi, and became a daimyō of 100,000 koku.
After Hideyoshi's death he clashed with Ishida Mitsunari and followed Ieyasu. Before the Battle of Sekigahara he took Gifu Castle with Fukushima Masanori and others, and in the main battle he fought Mitsunari's own troops with distinction. In Iyo, during his absence, Mōri forces invaded, but his senior retainer Tsukuda Kazunari repelled them with a night attack.
For his services he became daimyō of 200,000 koku in Iyo and, with Ieyasu's permission, began building a new castle on Mount Katsu. The next year he moved his base there and renamed the place Matsuyama. He had his retainer Adachi Shigenobu divert rivers and laid out the castle and its town. Matsuyama Castle is still a source of pride in Ehime.
In the previous year's winter campaign at Osaka, as a daimyō indebted to the Toyotomi, he was left to guard Edo, and his heir Akinari fought in his place. In this Summer Siege of Osaka he took the field himself, fighting with Kuroda Nagamasa in the army of the second shogun Hidetada and winning distinction. In this war the Toyotomi house fell.
At the ceremony in which Tokugawa Iemitsu, heir to the shogunate, first put on armor, he was honored with the role of attendant. When Iemitsu became the third shogun, Yoshiaki's rank was raised, and he later served as a guard when the emperor visited Nijō Castle. Though tied to the Toyotomi, he was deeply trusted by the Tokugawa.
When the Gamō of Aizu had their domain reduced for lack of an heir, Yoshiaki was moved to Aizu with over 430,000 koku. The shogun Iemitsu first meant to place Tōdō Takatora in Aizu, but Takatora is said to have recommended Yoshiaki, saying private discord was separate from affairs of state. Hearing this, the two reportedly reconciled and became close friends.
He fell ill and ended his life at his residence in Edo. An anecdote says that when a retainer broke one of a set of treasured plates, he smashed all the rest so that the retainer's name would not be remembered along with the mistake. His heir Akinari succeeded him but later lost the Aizu domain because of strife within the house.
Shibata KatsuieKuki YoshitakaTokugawa IeyasuTōdō TakatoraIshida MitsunariKuroda NagamasaTokugawa IemitsuFukushima Masanori
Fukushima MasanoriKatō KiyomasaMaeda ToshinagaHosokawa GraciaHosokawa TadaokiWilliam Adams (Miura Anjin)Ikeda TerumasaŌtani Yoshitsugu
People of the Sengoku/Azuchi-Momoyama period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.