The British royal appears on the newsstand edition of the September issue, while Chastain is on the cover of subscriber copies.
The unranked list of 40 individuals and couples includes royalty, people in the fashion industry, a smattering of actors, actresses and musicians, two football players, businesspeople and others. Among the honorees are "Today" co-anchor Matt Lauer, New York Giants' wide receiver Victor Cruz, rapper-producer Jay-Z, "60 Minutes" correspondent Morley Safer and New York philanthropist Lizzie Tisch.
The 73rd annual list -- the ninth since Vanity Fair was bequeathed it from its late founder, fashion publicist Eleanor Lambert -- includes the debut of Middleton's brother-in-law, Prince Harry, though her husband, Prince William, did not make the cut. This is the third time Middleton has been listed.
Actress Diane Kruger, musician Alicia Keys and actor Richard E. Grant all make their second appearances. Colin Firth, on the list for the second year in a row, appears this time with his wife, Livia, in the best-dressed couples category.
Despite a common misconception, no one tops the list. "The International Best-Dressed List is not ranked," Vanity Fair spokeswoman Beth Kseniak confirmed. "It never has been."