The agency was appointed following a competitive pitch, and is contracted until Christmas initially.
The brief will focus on the retailer’s seasonal product range.
Laura Wildish, WHSmith marketing manager, said: "Another Word impressed us with their response to our brief, which demonstrated how they would use creative tactics to engage audiences but ultimately drive them in-store in the lead up to Christmas."
Nichola Mughal, joint MD of Another Word, said: "We’re looking forward to bringing some festive cheer to the business with a campaign that delivers creatively and commercially."
WHSmith operates 1,300 stores across the UK.