She will start her new role on 2 June with a remit to oversee external and internal comms for the UK market, reporting to Kuoni UK MD Derek Jones.
For the past six years O’Reilly has run her own consultancy business, ROR Communications. Kuoni has been one of her clients.
Other clients include sustainable travel charity the Travel Foundation, Teletext Holidays, the Titanic Centenary Cruise, James Villas and Caribbean hotel group Elite Island Resorts.
She said that she had given clients notice she would be winding ROR Communications down and was making other arrangements for them to be looked after.
Before setting up her own consultancy O'Reilly was head of PR for TUI, the parent company of Thomson.
She said: "Kuoni became a client just over a year ago and I’ve been hugely impressed with the business and the team.
"With an expanding retail network, online presence and a partnership with John Lewis – as well as evolving its range of destinations, hotels, experiences and sectors, such as cruise – it’s an exciting time to be joining."