Morihiro Hosokawa was born on January 14, 1938, in Tokyo, Japan to the family of Morisada Hosokawa and Yoshiko Konoe. He is the eldest grandson of Moritatsu, 3rd Marquess Hosokawa, and the 16th Head of the Hosokawa clan. His maternal grandfather is the pre-war prime minister Prince Fumimaro Konoe. As a great-great-grandson of Prince Kuni Asahiko, he is a second cousin twice removed of the present Emperor, Naruhito. He is also a descendant of Christian heroine Gracia Hosokawa.
His family's wealth was so substantial that his grandfather’s private art collection could create a museum “similar to the Louvre,” Hosokawa once said. He never carried money because everything he bought was paid for by the butler.
Growing up, Hosokawa was surrounded by scholars, Buddhist masters, geisha, politicians, artists and other elites who came to visit his paternal grandfather, Moritatsu Hosokawa, a former politician with the upper house of Parliament. From him, Hosokawa learned to look for lessons in every encounter.