In an announcement to the stockmarket after it closed yesterday evening, Mike Ashley's firm said it had appointed the law firm, despite previous concerns from key investors over RPC's impartiality.
"This decision has been taken in the light of recent frustrations over delays in appointing an independent party other than RPC to lead the review," Sports Direct said in its statement.
The retailer has been under the media glare since 2015 when an undercover investigation exposed draconian working practices at its mammoth Shirebrook warehouse.
Sports Direct said it had twice accepted different candidates proposed by shareholder group the Investor Forum only for the parties to subsequently be withdrawn. It added:
We believe any further delays would place an unreasonable burden on the business at a time when the company should be fully focused on delivering its strategic priorities as we build towards our medium and long term aspiration to become the "Selfridges" of sports retail.
Investor concern over RPC stems from the fact that the firm provides services across several working streams to Sports Direct. It was initially engaged to undertake a review of working conditions following the revelations in 2015 and Sports Direct praised the firm for adopting "the highest standards in delivering the Working Practices Report".
RPC is the UK's 44th largest law firm with annual revenues of £94m, according to a ranking by law marketing firm Conscious.