Bill, who has been editor of Estates Gazette magazine since 1997, will leave the group in February next year, according to an internal memo, seen by Journalism.co.uk.
He will continue to contribute to the title in a weekly column starting in the spring.
"[I]t will truly be the end of an era," said Geoff Hadwick, publishing director of EG group, in the statement.
"You don't get to run such a successful title without a huge amount of personal and professional commitment.
"During Peter's decade or more at the helm, EG has dominated its market and we have launched and developed many new titles and online services with Peter’s guidance. It would be impossible to find a better ambassador to have on your side."
Bill's replacement has not yet been announced, a spokeswoman for RBI confirmed.
Last month parent company Reed Elsevier suspended the sale of its magazine publishing arm RBI, citing poor market conditions as the reason.
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