Marian Osgood Hooker was born in 1875 in San Francisco, California to Katherine Putnam Hooker and John Daggett Hooker. Her father was a wealthy businessman connected to the hardware industry and iron works. He served as vice president of Baker Iron Works, and was president of Western Union Oil Company for a time. In 1886, Hooker moved his family from San Francisco to Los Angeles in order to pursue business opportunities there. In Los Angeles, the Hooker home entertained prominent guests, such as John Muir the conservationist, George Hale the astronomer, artists, and other intellectual figures.

Marian attended the Marlborough School for Girls, an exclusive preparatory school in Los Angeles. There, she studied art history and became interested in photography, a common hobby for a young woman of wealth and leisure at the time. She began visually documenting her family, classmates, home life, friends, and school play productions. She even printed her own glass plate negatives, demonstrating a skill and aptitude for photography, and foreshadowing the amateur photographer she would become.

After graduating, Marian and her mother took an eight-month excursion to Europe in 1896. While in Europe, Marian photographed European architecture, street life, villages, and other sites, showing a particular interest in Italy. Between 1899 and 1922, Marian and her mother took four other extended European trips. Katherine wrote several noteworthy works about their travels with Marian's photographs accompanying the text, including Wayfarers in Italy (1902) and Farmhouses and Small Provincial Buildings in Southern Italy (1925). The images in the latter text supposedly influenced several Southern California architects, such as Myron Hunt.

Besides Europe, Marian also enjoyed traveling around the Sierra Nevada. In 1903, John Muir asked her to hike up Mt. Whitney with him and small group of people, making her the first woman to scale the mountain. Mt. Whitney had been named after her maternal great uncle, a prominent geologist.

Marian graduated from the University of California, Berkeley in 1910 with a degree in medicine. The University of California appointed her as the Assistant Medical Examiner in 1912. Around this time, Marian's father passed away. After Hooker's death, Katherine moved to San Francisco where Marian moved in with her. While a physician, Marian wrote several books on medicine, but she eventually left the profession to take care of her mother. In 1924, they moved to Santa Barbara. Although they never traveled abroad again, both women took automobile trips around California, always with a camera in hand.

Marian passed away in 1968 in Santa Barbara.