Havas' remit includes national and regional PR support for the brand, with the account team reporting into Deliveroo head of PR Kate Thomas.
Deliveroo now has a presence in more than 70 cities across the UK after launching in London in 2013 - and in 11 other countries across the world.
According to an FT article earlier this year, Deliveroo's "network of more than 3,000 self-employed cyclists delivers food for more than 2,500 London restaurants" - and it is thought to be worth around £490m, although it faces potential competition from Uber, which recently launched its UberEats service.
Brian Beech, MD of Havas PR UK, said: "The business is making an investment in PR support as part of a wider campaign to raise awareness of the expanding delivery service. It’s a really exciting contract for Havas to win, in an area where we have strong credentials."
Havas PR UK has offices in London, Manchester and Edinburgh, and its food-and-drink portfolio already includes brands such as Greggs and Kellogg's - as well as Asda, for whom it handles regional PR and will continue to do so even after the supermarket chain announced the end of its relationship with Freud Communications.