Mr Parkes is a former director at Finning (UK). He took over at Hewden in 2009, leading the business after the sale to private equity company Sun European Partners.
Mr Parkes said: "It has been my pleasure to lead Hewden over the past six years, through challenging times we have radically reorganised and rebuilt the business, relentlessly executing our strategy so Hewden is best placed to take advantage of the recovering market."
The company said that a further announcement regarding a successor would be made next month.
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