In 1589, Hidetada's mother fell ill, her health rapidly deteriorated, and she died at Sunpu Castle.

In 1590, the new ruler of Japan, Toyotomi Hideyoshi enlisted Tokugawa Ieyasu and others in attacking the domain of the Hōjō in what became known as the Siege of Odawara (1590).

But after Hideyoshi died in 1598 and Hideyori became nominal ruler, the regents forgot all vows of eternal loyalty and were soon vying for control of the nation.

Ieyasu then ordered Hidetada to march to Sekigahara in anticipation of the decisive battle against the Western faction.

But the Sanada clan managed to tie down Hidetada's force, so he arrived too late to assist in his father's narrow but decisive victory.

On 3 December 1601, Hidetada's first son, Chōmaru (長丸), was born to a young maiden from Kyoto named Onatsu.

In September 1602, Chōmaru fell ill and died; his funeral was held at Zōjō-ji temple in Shibe.

To avoid his predecessor's fate, Ieyasu established a dynastic pattern soon after becoming shogun by abdicating in favor of Hidetada in 1605.

Ieyasu retained significant power until his death in 1616; but Hidetada nevertheless assumed a role as formal head of the bakufu bureaucracy.

When this failed to quell Hideyori's intrigues, Ōgosho Ieyasu and Shogun Hidetada brought an army to Osaka.

Historian Michifumi Isoda opined that the total isolationism policy implemented by Hidetada has gradually weaken the military of Japan under Tokugawa shogunate in the long run.