The move comes after 66-year-old Marchione suffered serious complications from an operation on his shoulder earlier this month.
Fiat Chrysler say British-born Manley will continue with the strategy outlined by Marchionne last month which will assure the company’s “strong and independent future”.
Marchionne is credited with rescuing Fiat and Chrysler from bankruptcy since taking the wheel at the Italian carmaker in 2004.
He had been due to step down from the combined group next April.
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