Scott will report into Elvis founder, Martin Semmens.
David Bainbridge who continues as joint chief executive of the agency group will now focus on international development, focusing on growing the agency across North America and Asia.
At Elvis, Scott will focus on driving the agency’s direct and data capabilities, and will support the direction of Elvis globally.
She will also be responsible for the day-to-day running of the agency alongside executive creative director John Treacy.
Scott will also work alongside Tanya Brookfield who has been promoted to deputy managing director from client services director.
The appointment marks a return to the industry for Scott, who was previously the chief executive of now defunct agency, Craik Jones Watson Mitchell Voelkel.
The agency merged with Proximity in 2008 and Scott left the industry to launch British rainwear brand, La Mack London.
Martin Semmens, founder of Elvis said: "Fiona arrives at Elvis at an exciting time in our growth. She brings with her an impeccable pedigree, strong leadership credentials and a deep understanding of the future of our space.
"She will be a great asset to our leadership team here."