Justin Kaplan was born in Manhattan, New York on September 5, 1925. He received a bachelor's degree in English from Harvard University, followed by graduate work in the field there, but he left before earning a doctorate to work as a freelance writer and book editor. His first book, Mr. Clemens and Mark Twain, won the Pulitzer Prize for biography in 1967 and a National Book Award. His other works include Lincoln Steffens: A Biography, When the Astors Owned New York: Blue Bloods and Grand Hotels in a Gilded Age, and Walt Whitman: A Life, which won a National Book Award. He also wrote books with his wife Anne Bernays including The Language of Names and Back Then: Two Lives in 1950s New York. He was the editor of Bartlett's Familiar Quotations. He died from complications of Parkinson's disease on March 2, 2014 at the age of 88.