Scanlan has been appointed director of UK public affairs for Arriva and takes up his role on 11 January.
De Leo is head of public affairs at FleishmanHillard while Scanlan is her opposite number at Fishburn.
Scanlan told PRWeek he had accepted the role at Arriva before the merger of Fishburn with FleishmanHillard was announced.
He said: "I’m really looking forward to taking up my new challenge with Arriva. I think the merger of Fishburn and FleishmanHillard will create a public affairs powerhouse."
At Arriva, Scanlan will lead on political and stakeholder coordination across the group’s bus and rail businesses and will report to Alison Cole, the director of communications.
Cole said: "I am delighted that Rory will be joining Arriva as we continue to focus on growth opportunities in both the bus and rail markets across the UK and mainland Europe. He brings a wealth of public affairs experience from a variety of sectors and from working with many high-profile businesses."
Ali Gee, who will be the deputy chief executive of FleishmanHillard Fishburn and is currently chief executive of Fishburn, paid tribute to Scanlan’s work at the agency.
She said: "Rory has been an invaluable member of the Fishburn business for the past eight years and we’re very sad to see him go. Under his leadership Fishburn won Campaign of the Year and PA Consultancy of the Year. He has been a great mentor to his team too. We would have loved to bring him with us as we begin our partnership with FleishmanHillard but as he takes up this exciting role he leaves with our very best wishes for the future."