PRWeek reported in June that six agencies were in the running to pick up the new account, which is believed to worth six figures annually.
Hope&Glory is Argos' first retained consumer PR account since Sainsbury's acquired the chain for £1.4bn last year.
Hope&Glory's win follows news this week that Sainsbury's corporate affairs director Louise Evans had been made redundant in a restructure of the supermarket's comms and corporate affairs functions.
Hope&Glory's brief includes consumer PR across Argos' consumer electronics, toys and nursery and jewellery divisions. The agency will also work on campaigns highlighting the brand's position as a UK leader in online retail.
Agency managing partner James Gordon-MacIntosh, who is leading the account, said: "Argos is a great British retail success story and is now as much an online powerhouse as a high street stalwart.
"We're looking forward to developing creative campaigns that ensure the public's perceptions catch up with Argos's reality and that the brand is recognised as the pioneer it has become."