Diamant spent her early childhood in Newark, New Jersey, and moved to Denver, Colorado, when she was 12 years old. She attended the University of Colorado at Boulder and transferred to Washington University in St. Louis where she earned a bachelor's degree in Comparative Literature in 1973. She then went on to receive a master's degree in English from Binghamton University in 1975.

Diamant started her writing career in 1975 as a freelance journalist, for which she won awards. Her articles have been published in the Boston Globe magazine, Parenting magazine, New England Monthly, Yankee, Self, Parents, McCalls, and Ms.

She branched out into books with the release of The New Jewish Wedding, published in 1985, and has since published seven other books about contemporary Jewish practice. Her debut as a fiction writer came in 1997 with The Red Tent, followed by the novels, Good Harbor and The Last Days of Dogtown, an account of life in a dying Cape Ann, Massachusetts village in the early 19th century. Her newest book, Day After Night, is a novel about four women who survived the Holocaust, and find themselves detained in a British displaced persons camp.

Diamant is the founding president of Mayyim Hayyim: Living Waters Community Mikveh and Education Center, a community-based ritual bath in Newton, Massachusetts.

She lives in Newton, is married, and has one adult daughter.

Fiction

• The Red Tent (1997)
• Good Harbor (2001)
• The Last Days of Dogtown (2005)
• Day After Night (2009)

Non-fiction

• The New Jewish Wedding (1985, revised 2001)
• Living a Jewish Life (1991, revised 2007)
• Pitching My Tent (1995, 2005)
• Choosing a Jewish Life (1998)
• Saying Kaddish: How to Comfort the Dying, Bury the Dead, and Mourn as a Jew (1998)
• How to Be a Jewish Parent (2000)
• The New Jewish Baby Book (1988, revised 2005)

Author Andrew Neiderman dedicated his 1990 novel The Devil's Advocate to Diamant.