The brief will see Shine operate an integrated campaign combining social, search, PR, creative, media buying and planning to increase awareness and business opportunities for the New Zealand-based company in the UK.
Shine will work with Xero's existing PR consultancy Whiteoaks, which handles trade, technology, accounting and regional media for the company.
Shine was appointed prior to a competitive pitch.
Xero has doubled its customer base year on year since its launch in 2008. Chief marketing officer Andy Lark said: "Shine has great experience delivering integrated marketing campaigns for some of the UK’s leading brands and we’re looking forward to working with the team as they support us in our strategy of continued growth."
Erika Kessel, director at Shine, said: "It’s incredible what [Xero] has achieved in the southern hemisphere, and we are looking forward to further strengthening its position in the UK market."