Maguire is married to American painter Andy Newman, in one of the first same-sex marriages performed in the state of Massachusetts.

His mother died from complications suffered giving birth to him, which prompted his father to send him to live with an aunt.

In 1987, Maguire co-founded a nonprofit educational charity, Children's Literature New England, Inc., and was co-director for twenty-five years.

In 2005, ten years after its publication, Wicked spent 26 weeks on the New York Times bestseller list.

[1] Maguire met American painter Andy Newman in 1997 at the Blue Mountain Center, an artists' and writers' colony.

Maguire and Newman were married in June 2004, shortly after same-sex marriage became legal in Massachusetts.