Cleaves was the first woman physician to regularly treat mental illness at that institution, and subsequently served as a member of the board of trustees.

In 1885, Cleaves was appointed to the University of Iowa Medical Department's examining committee, "perhaps the first woman to serve in that capacity in the United States.

Her father was of Dutch and English descent, and her mother of Scotch and Irish ancestry, but both had been born in the United States.

[4] Cleaves was educated at public schools and eventually enrolled in the University of Iowa, but was unable to complete her undergraduate degree due to financial difficulty.

In 1870, Cleaves began to study medicine and enrolled in Medical Department of the University of Iowa against her family's wishes.

[4] Shortly after graduating, Cleaves was appointed second assistant physician in the State Hospital for the Insane in Mount Pleasant, Iowa.

[4] While practicing medicine in Davenport, she became a member of the Scott County Medical Society, being the second woman to gain admission to that body.

[5] In 1879, the board of trustees of the State Asylum for the Insane chose her their delegate to the National Conference of Charities, which that year met in Chicago, Illinois.

It attracted widespread attention, and was printed in a volume, Lunacy in Many Lands, which was published by the Government of New South Wales.

She witnessed operations in general hospitals in England, France, and Germany, and in Paris, she was for several months a regular attendant at lectures and clinics.

After returning to the United States, she opened a private home for the reception of patients in Des Moines, Iowa, conducting also an office practice in connection with her other work.

[5] In the medical fields of radiation oncology and gynaecology, Margaret Cleaves is remembered as the first physician to successfully apply radium in the treatment of cancer of the uterine cervix.

[6] In her seminal paper of October 1903, she wrote: "...an inoperable primary pelvic case of epithelioma, involving the cervix, anterior and posterior vaginal walls, almost to the introitus; rectum, bladder, and both broad ligaments."

(page 605) The patient was treated first by a combination of x-rays and ultraviolet light, followed by intravaginal insertion of one gram of bromide of radium in a sealed glass tube.

Five days subsequent to the use of radium, no bleeding, no odor, no discharge, no ulceration, and vaginal and cervical mucous membrane normal in appearance."