The win is part of a wider consolidation of the $130m (£67m) Staples brief, including the retention of the $100m US media account by the WPP-owned agency and victory in the Canadian market, snatching the estimated $19m media account from Interpublic's Universal McCann in the territory.
Last October, Staples awarded its £6m creative account to Euro RSCG London as part of an expansion of the brand beyond stationery. The firm has recently diversified into product ranges such as office furniture and satellite navigation systems.
The retailer opened its first UK store in Swansea in 1993 and now owns a network of 85 stores across the country, with plans to open five every year.
The retailer is also looking to boost the presence of its online purchasing site
Staples set a trend to enable small firms to buy their office supplies at cheaper prices, which had previously been reserved for larger corporations. The company has more than 50,000 employees globally and currently has 7,000 product ranges.
The agency is now expected to place the account into its bespoke retail division, adding to roster clients including Ikea.
MediaCom is also part of the pitch list for high street retailers HMV Group, which is looking for an agency to work across the consolidated media account for its HMV and Waterstone's brands. Other agencies pitching for the account include Starcom and incumbents OMD and PHD.
The decision on the account is expected by the end of the month.
MediaCom confirmed that it had picked up the UK account as part of the larger multi-territory consolidation.