She founded the Iwamoto Mari String Quartet and was a professor at the Tokyo Academy of Music.

Born in Japan to a Japanese father, Masahito Iwamoto, and an American mother, Marguerite (nee Magruder).

From 1946 to 1949, she was a professor at the Tokyo Academy of Music, resigning the post in 1949 in order to spend a year in the USA.

She stayed there in a year and half, and took lessons by George Enescu in Chicago, and Louis Persinger in New York at The Juilliard School.

[3] In addition, She founded the Iwamoto Mari String Quartet in 1967, with violinist Tomoda Yoshiaki, viola player Suganuma Junji and cellist Kuranuma Toshio; the quartet won a special prize at the Suntory Music Award in 1979, shortly prior to Mari's death from cancer on 11 May 1979.