The novel is one of the last literary classics to become digitized. The book sells more than 1 million physical copies each year, and has sold a total 30 million since its initial publication in 1960.
Lee, who turned 88 on Monday, calls the ebook "Mockingbird for a new generation." She professes herself "old-fashioned," and says that she still loves "dusty old books and libraries."
The author recently regained the rights to her novel in September 2013. Lee had turned over control to her former literary agent, Samuel Pinkus, in 2007, but later sued for improper collection of royalties.
The To Kill a Mockingbird ebook will be released July 8, just days before the 54th anniversary of its publication. A Sissy Spacek-narrated digital audio version will also debut the same day.