Miriam Coles was born into a Long Island family going back to the 17th Century. She was descended from Robert Coles who immigrated to America with John Winthrop in 1630. She was educated at St. Mary's Hall-Doane Academy (now Doane Academy) in Burlington, New Jersey, and Mme. Canda's Girls' School in New York City. On April 20, 1864, she married Sidney Smith Harris (1832–1892) of New York, a lawyer, with whom she had two children, a son, Sidney and a daughter, Natalie.
After the death of her husband in 1892, she spent most of her time in Europe, dying in Pau, Pyrénées-Atlantiques, France in 1925.
A devout Episcopalian, who late in life, some sources suggest, converted to Roman Catholicism, But, New Catholic World, Volume 86 (1908), in a review of Tents of Wickedness wrote, "The keen appreciation, the deep sympathy, shown in the telling of that story bespeak a personal note, something perhaps of what the author herself has experienced in her way to the Catholic Church." In Catholic world, Volume 68 (1899) it states, "we have received the following notice of an author, Mrs. Miriam Coles Harris, who entered the one true church about two years ago ... Unlike most American authors, Mrs. Harris has not been a contributor to magazines, having done no writing outside of her novels with the exception of two devotional books written while she was a member of the Anglican Church. Her most recent publication, A Corner of Spain, is therefore somewhat of a departure ... When Mrs. Harris made the visit to Spain, she was not a Catholic." However that information is inaccurate, she had written many magazine articles. She published a number of children's stories with a religious theme, prior to her first novel. These included Philip and Arthur (1859), Ash Wednesday in the Nursery (1859) and Saturday Afternoon (1859).
Coles-Harris also wrote many magazine articles. These include "A Playwrights Novitiate" in the Atlantic Monthly (1894), on writing for the stage, and another in Lippincott's Magazine (1893), criticizing the undue exaltation of what she called "Seventh Commandment novels".
Her first novel was Rutledge, released in 1860. It has been described as the first "fully-American Gothic novel." The narrator is an orphaned teenager whose aunt sends her to live with her new guardian, Arthur Rutledge, in his ancestral home. As in the case of Jane Eyre before it, and Rebecca some eighty years later, the mansion holds a dark secret. She falls in love with Rutledge, but misunderstandings and jealousy lead her to behave antagonistically, becoming engaged to a young man with serious emotional problems and a horrible past. The author had written several chapters before she realized that she had not given a name to the heroine. Then it occurred to her that if she could finish the book without supplying a name, the idea would be unique.
Coles' first novel and work up to that time were published anonymously. Part of an article in the Brooklyn Daily Eagle (January 18, 1891) states,
"One of the notable points in the history of American literature was the great success of the novel 'Rutledge,' published in 1860, the long continued discussion and inquiry as to its authorship and the remarkable claims of two or three women in various parts of the country to have written it. The book ran through edition after edition, and was talked about with equal vigor in the newspaper columns and in drawing rooms and boarding schools. While this furore was going on the mysterious author of "Rutledge", a young girl, Miriam Coles, was living quietly in her home at Oyster Bay and listening gravely to the denials of her family that she had written the book or had anything to do with it. The secret was well kept until two other books from the same pen had appeared, 'The Sutherlands' and 'Louie's Last Term at St Mary's', and until Miss Coles had married a New York lawyer, Sydney S Harris. Mrs Harris' mother was a Weeks, and the family homestead was the present house of John A Weeks, at Oyster Bay. Here Miss Coles, who was born at Dosoria, on East Island, wrote the first part of Rutledge, with no confidante but her mother.
(This article was reprinted in abbreviated form in Book News (October, 1893))
The following review appeared in The Eclectic Magazine of Foreign literature, Science, and Art, Volume 54 - Page 859 (1891)
A NOVEL WITH A TAG TO IT, An Utter Failure, A Novel, By Miriam Coles Harris, Author of Rutledge, etc., New York, D Appleton & Co.
"The author of 'Rutledge' has not been as prolific in literary production as one might wish, but her last book, now before us proves, that her pen has not lost its cunning. The story is a pathetic one and its melancholy is but slightly relieved by any sunshiny pictures of life. We do not quite see any sufficient motive for Rachel's marriage to Count Paolo Buonamici on her Italian visit, except that the American girl was blinded and dazzled by the general fascination of Italy, for she does not love the man -- an empty-headed, cold-hearted, sterile-natured man, who conquers ber by the brief passion of temperament and a certain clinging persistence like that of the jelly fish. The Italian count wins the girl and her fortune, and finally comes to America to enter the banking business, fully developed in the most mean and despicable of all passions -- avarice. The upshot is that he makes his wife exquisitely miserable, alienates her two children, and when the separation finally occurs, takes them away from her forever, and she dies of a broken heart. Whether or not the author intends to emphasize, in this vividly sad picture of a ruined life, the great danger the American girl runs in marrying a foreigner, specially if in so doing she puts all her property in his hands, we do not know. Certainly this thought is powerfully impressed on the mind, and it seems to stand out in letters of fire between the lines. An added element of tragedy gives its touch of interest in the discovery, too late, by Rachel that she has a heart, and that it beats for a man whom she might have married but for one of those trivial accidents which seem nothing at the time, but which are weapons more effective in the hands of that stern and veiled Anangke who was fabled to stand behind the thrones of even the gods, than the thunderbolts of Jove himself. The true-hearted man and the no less true-hearted woman go apart from each other to lives of accumulated misery that not even the shadow of shame may come to them. Mrs Harris has given the public a touching and significant book, worked out with a nice sense of spiritual portraiture, and made artistically effective by an incisive and agreeable style."
Her other works include The Sutherlands (1862), Louie's Last Term at St. Mary's (1864), Frank Warrington (1863), Richard Vandermark (1871), Roundhearts, and other Stories (1871), A Perfect Adonis (1880), Missy (1882), Dear Feast of Lent (1883) and The Tents of Wickedness (1909),