Avi and his twin sister Emily Wortis Leider (also a writer) were born in New York City to Joseph Wortis, a psychiatrist, and Helen Wortis, a social worker. In the year after Avi's birth, his family moved to Brooklyn. When he was young his sister gave him the nickname "Avi." Two of Avi's grandfathers were writers, and one grandmother was a playwright. In interviews, he recalled his mother reading to him and his sister every night, and going to the public library on Fridays. He is also the first cousin of the Academy Award-winning actor Alan Arkin.

Avi's parents transferred him from Stuyvesant High School to Elisabeth Irwin High School, a smaller private school. There he studied with a tutor, Ella Ratner, whom he credits for his writing success.

Avi has written more than 60 books. He has written books for different age groups and in many different genres including historical fiction, fantasies, comedies, mysteries, ghost stories, adventure tales, realistic fiction, and picture books. Avi has won awards for his books, including a Newbery Honor for The True Confessions of Charlotte Doyle in 1991 and another for Nothing But the Truth in 1992. His fiftieth book, The Cross of Lead, was awarded the Newbery Medal in 2003. Avi's book, "Iron Thunder," about the ironclad Monitor and its battle with the CSS Virginia in Hampton Roads, Va., was selected as the 2009 Beacon of Freedom Award winner by Williamsburg Regional Library and Colonial Williamsburg Foundation. He accepted the award at the Williamsburg Library on Friday, Oct. 16 at 7:30 p.m. As of the end of 2009, Avi will have published 70 books, all written for children/young adult. In 2006 Avi wrote a sequel to Crispin: The Cross of Lead titled At the Edge of the World.

After living in Providence, Rhode Island in the 1980s and 1990s, Avi now lives inDenver, Colorado, with his wife, Linda Cruise Wright. He has adult children.

• Sherwood Anderson's The Triumph of the Egg : and experiment in production styles, 1962 (dissertation)
• Things That Sometimes Happen, 1970
• The Adventures of a Rather Small Snail, 1972
• No More Magic, 1975
• Captain Grey, 1977
• A Massachusetts Adventure, 1978
• Night Journeys, 1979
• A Bibliographic History, 1979
• Encounter At Easton, 1980
• History of Helpless Harry: to which is add a variety of amusing and entertaining adventures, 1980
• Man From The Sky, 1980
• Who Stole The Wizard Of Oz?, 1981
• A Place Called Ugly, 1981
• Sometimes I Think I Hear My Name, 1982
• Shadrach's Crossing, 1983
• Smuggler's Island, 1983
• Devils Race, 1984
• S.O.R. Losers, 1984
• The Fighting Orgy, 1984
• Bright Shadow, 1985
• Wolf Rider, 1986
• Romeo & Juliet, Together and Alive at Last, 1987
• A Tale of Ghosts 1988
• The Man Who Was Poe 1989
• The True Confessions of Charlotte Doyle, 1990
• Nothing But the Truth, 1991
• Windcatcher, 1991
• Blue Heron, 1992
• Who Was that Masked Man Anyway?, 1992
• City of Light, City of Dark, 1993
• Punch With Judy, 1993
• The Barn, 1994
• The Bird the Frog and the Light : A Fable, 1994
• Poppy, 1995

• Tom, Babbette & Simon, 1995
• Beyond the Western Sea: The Escape from Home (Book I), 1996
• Beyond the Western Sea: Lord Kirkle's Money (Book II), 1996
• Finding Providence: The Story of Roger Williams, 1997
• Keep Your Eyes on Amanda, 1997
• What Do Fish Have To Do With Anything? and other stories, 1997
• Talk to Me, 1997
• Perloo the Bold, 1998
• Poppy & Rye, 1998
• Abigail Takes the Wheel, 1999
• Midnight Magic, 1999
• Ragweed, 1999
• Amanda Joins the Circus, 1999
• Stories for a New Millennium, 1999
• Ereth's Birthday, 2000
• The Christmas Rat, 2000
• Don't You Know There's a War On?, 2001
• Prairie School, 2001
• The Good Dog, 2001
• The Secret School, 2001
• The Cross of Lead, 2002
• Silent Movie, 2003
• The Mayor of Central Park, 2003
• Never Mind, 2004
• The End of the Beginning: Being the Adventures of a Small Snail (and an Even Smaller Ant), 2004
• Poppy's Return, 2005
• A Fable of Medieval Magic, 2005
• Five Tales of Transformation, 2006
• At the Edge of the World, 2006
• The Traitors' Gate, 2007
• Iron Thunder, 2007
• The Seer of Shadows, 2008
• A Beginning, a Muddle and an End, 2008
• Poppy and Ereth,2009
• Murder at Midnight, 2009
• The End of Time, 2010