Seven Dials won the brief following a four-way pitch. US-based HB Agency previously led the account.
Seven Dials director Claire Curran will work with CEO Alan Clarke to help build the brand and become a leader in the homestay travel market.
The agency will handle all corporate comms as well as supporting the in-house comms team.
Simon Kelner, chief executive at Seven Dials, said: "This is a business that is driven by ambition, innovation and excellence and strives to put hosts and guests at the heart of everything it does. It is our job to tell the Homestay story to a wider audience and help differentiate it from other accommodation websites in the marketplace."
Homestay.com was launched in 2013 and is based in Dublin.