Newman-Hall, who starts his new role today (6 July), rejoins the property in Oxfordshire after having previously been general manager for five years between 1999 and 2004.
He replaces Lewis, who left two weeks ago to "pursue other things".
He previously worked as acting general manager at Stapleford Park in Leicestershire, where he oversaw a major refurbishment, as well as general manager of Bovey Castle in Devon, a role he left after just six weeks in 2005.
Newman-Hall said he was excited about his return to Le Manoir.
"It's a very satisfying feeling to rejoin Raymond and the team that I was close to for so long," he said. "There have been tremendous developments at the house and I look forward to playing my part in its future."
Chef patron Blanc added that it was "fitting" to welcome Newman-Hall back to celebrate the property's 25th anniversary: "A person who understands the heart of any house is hugely important and I am thrilled to be working with Philip again."
By Gemma Sharkey
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