Margaret Louise Coit was born 30 May 1919 in Norwich, Connecticut, to Archa Willoughby Coit, a stockbroker, and Grace Coit (nee Trow), the principal of a private day school. Two years later, Margaret's sister Grace was born with Down Syndrome. Caring for Grace would take up much of Coit's adult life.

At the start of the Great Depression, Coit's family moved to Greensboro, North Carolina, where Coit attended Curry School, a training school located on the grounds of Woman's College (now the University of North Carolina at Greensboro, or UNCG). Coit graduated Curry High in 1937 and went on to study history and English at Woman's College, where she edited the college magazine, wrote for the school paper, and studied with professors such as Caroline Tate and Mildred Gould.

Meanwhile, Coit's parents had moved to West Newbury, Massachusetts, and after graduating in 1941, she moved north to work as a reporter for the newspapers of surrounding towns -- the , , and . Over the next nine years, Coit also performed extensive research on South Carolina statesman John C. Calhoun, in whom she had developed an interest while still a school child at Curry. was published to critical acclaim in 1950, and Coit was awarded the Pulitzer Prize for biography in 1951.

As a result of the critical acclaim for , Coit won a staff appointment to the University of New Hampshire Writers Conference, where she met Lloyd Haberly, a poet and the new Dean of Fairleigh Dickinson University. Haberly invited Coit to teach at the university's Rutherford branch, where she began as a visiting writer in the English department in 1950, then became a professor of social science. Over the next decade Coit would also teach at the University of Colorado and Breadloaf writers conferences, and write articles and reviews for various national publications, such as , the the , and . In 1959 Woman's College bestowed upon Coit an honorary Doctor of Letters.

Coit's treatment of Calhoun also drew the attention of Bernard Baruch, who requested she write his biography next. Coit spent seven years working closely with Baruch, combing through his personal papers and interviewing his associates, among them top political figures of the day. Unfortunately, Baruch did not agree with the final product, and withdrew permission to quote from his personal papers and friends. However, the attorneys at Houghton Mifflin gave the go-ahead, and was published in 1957. It was named a Book of the Month selection by the National Council of Women in 1958. Although Baruch later extended an olive branch to Coit, her negative experience with writing a biography of a living person caused her to refuse to do so ever again; she even turned down an invitation to write the life story of Eleanor Roosevelt, whom she greatly admired.

In the 1960s, Coit found success writing historical non-fiction for children. In 1961 her won the Thomas Edison Award, and she followed that up with in 1965 and in 1967. She did not stick strictly to the youth market, however, and also managed to contribute two volumes, entitled and , to a Time-Life series on United States history, both in 1963. During this time, Coit also traveled overseas for the first time. In the summer of 1964, she sailed to the United Kingdom to deliver talks on the American political scene.

In 1970 Coit was recruited to edit . In 1977 Phi Alpha Theta conferred membership upon her for "conspicuous attainments and scholarship in the field of history." In 1978, Coit married farmer and politician Albert Elwell, whom she had first met at a West Newbury town meeting in 1954, and moved to Strawberry Hill Farm, where she helped tend the land and care for Albert's five grandchildren. Although almost eighty years old, Albert remained very active in local politics, and Margaret (now Margaret Coit Elwell) herself served as moderator at town meetings.

Although Margaret did not publish any books in the 1980s, she continually researched and wrote about topics that interested her. She worked on an adult-level book about Andrew Jackson and spent years developing a book entitled ; though it was never finished, she did teach a course of that same name in 1981. In 1984, Margaret was given the Rutherford Campus Faculty Award to recognize her years of teaching at Fairleigh Dickinson. Soon after, she retired in order to find work closer to home, and from 1985 to 1987 she taught a course on the American presidency at Bunker Hill Community College in Charlestown.

Margaret Coit died in 2003.