Mannion is currently executive editor of FHM and has worked at the magazine for three years. He takes up the new role on March 1.
The former FHM.com editor, Chris Mooney, moved to the position of editorial director of FHM International in November 2004.
FHM.com, one of the longest established online magazine brands, was also one of the first to begin charging for elements of its content when it introduced paid-for content in 2002.
James Carter, publishing director of FHM UK, said: "This appointment, combined with increased investment over the next few years, will see FHM.com strengthen its market leading position and broaden the premium content offering to many users."
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