Born and raised in a suburb of Chicago, Illinois, Mitchard is the daughter of a plumber and a retail clerk. She studied creative writing for three semesters under Mark Costello (author of The Murphy Stories) at the University of Illinois at Urbana-Champaign.
She became a newspaper reporter in 1976, eventually achieving a position as lifestyle columnist for the Milwaukee Journal Sentinel newspaper. Her weekly column, The Rest of Us: Dispatches from the Mother Ship, appeared in 125 newspapers nationwide until she retired it in 2007. Mitchard is a contributing editor for PARADE, and Wondertime, and is featured regularly in Reader's Digest, Good Housekeeping, Hallmark, and other publications.
Mitchard married Dan Allegretti, a reporter for The Capital Times, and the couple had four children (Jocelyn, Robb, Dan, and Marty). After 13 years of marriage, Allegretti died of colon cancer at the age of 45 in 1993.
After the death of Allegretti, while working for the freelance Milwaukee Journal Sentinel and a part-time public relations position at the University of Wisconsin—Madison, she started writing her first novel, The Deep End of the Ocean. The idea for the story had come to her in a dream in the summer of 1993. She is an alum of the Ragdale Foundation, an artist's colony in Lake Forest, Illinois, where she went to write the first two chapters on the encouragement of author Jane Hamilton. After finishing the first six chapters, 70 pages, she sold the book to Viking Press for $500,000, in December 1994, for that book and a second one to be written later (The Most Wanted)."FYI". - Milwaukee Sentinel. - December 17, 1994....Steinberg, David. - "Author Has Oceans of Good Luck". - Albuquerque Journal. - August 10, 1997.
Bolstered by being featured by Oprah, the novel sold close to 3 million copies by May 1998. It has been Mitchard's only #1 New York Times Bestseller, on the list for 29 weeks, including six weeks at number 1. The book had originally reached number 14, and then dropped off the list, but after being selected by Winfrey, sales jumped. The paperback would spend 16 weeks on the list. The film rights were sold for $300,000.
But all of her other novels have been bestsellers as well as garnering critical acclaim—particularly for The Most Wanted, Cage of Stars and The Breakdown Lane. The Most Wanted was nominated for Britain's Orange Prize for Fiction and Cage of Stars for Britain's Spread The Word Prize.
In 2004 Mitchard published her first book for children and young adults. Her first children's picture book, Baby Bat's Lullaby, appeared in 2004 from HarperChildren's. Her two middle-grade novels, also published by HarperChildren's, Starring Prima!: The Mouse of the Ballet Jolie, and Rosalie, My Rosalie: The Tale of a Duckling appeared in 2004 and 2005. Her second children's picture book, Ready, Set , School!, appeared in 2007.
Now You See Her, Mitchard's first Young Adult novel, was published in 2007 by HarperTeen. All We Know of Heaven (HarperTeen) appeared in spring 2008, and the first in a series of Young Adult mysteries, The Midnight Twins (Razorbill/Penguin), based on the bewildering clairvoyant gift of twins Mallory and Meredith Brynn, debuted in summer 2008.
Mitchard lives south of Madison, Wisconsin, on 110 acres of farmland now planted as prairie, with her husband, Christopher Brent Sornberger (an artist-carpenter) and their seven children: Rob, Dan, Marty, Francie, Maria ("Mia" or "Mira"), Will and Atticus.
Mitchard and Sornberger acted together in the theatre play Love Letters by A.R. Gurney at the Performing Arts Center at Oregon High School in 1999.