Morizono began drawing as a child, but her professional debut came rather late compared to many other mangaka. She was already 23 when she won Shogakukan's award for new artists in 1981.
Morizono made her debut in 1981 with "Crazy Love Hisshouhou" on Bessatsu Shoujo Comic. For the first six years she drew shoujo manga, and even dabbled in gag manga for young men. Then, with the boom of ladies' manga, she started to draw for mature female readers and she has been a very popular Ladies mangaka since 1987. By the middle of the nineties, when the boom began to subside, she started thinking about drawing softer manga or even manga for a male audience. Her real name is Mizoguchi Hiroko. Her penname was coined when she attempted together with an editor to come up with something feminine and catchy.

Morizono Milk was married to Murasaki Hyakuro until his death.