The company edged ahead of its main competitor with 32.71% dollar share and 36.55% unit share against Marvel Comics' 31.96% and 35.45%.
Robert Kirkman's The Walking Dead #100 - published by Image Comics - was the top-selling single issue of the month with an estimated 383,000 copies.
It has become the best-selling issue since 1997's The Darkness #11, and the first non-Marvel or DC comic to top the chart since Image's Masters of the Universe #1, which was published in November 2002.
DC filled six of the top ten slots, with Marvel's Avengers Vs. X-Men taking the other three.
Marvel has habitually topped the publishers chart since Diamond Comic Distributors began releasing its figures, but has fallen behind DC more frequently since the latter's New 52 relaunch last September.
DC's Batman: Earth One was the best-selling graphic novel of July.