She will manage the agency’s digital strategy and output, as well as research and planning across all platforms.
Billingsley previously ran Big Cat Media, her own digital consultancy, which specialises in helping print-focused businesses become more "digital-centric".
Before this she was the publishing director for mobile devices at Immediate Media where she launched the BBC magazine titles as digital magazines.
She helped with the launch of Times Online, heatworld, Closer Online and Red Magazine’s websites. Billingsley also managed the evolution of the Elle UK, Digital Spy, Sugarscape, Current TV and Radio Times websites into profit making businesses.
She said: "The very definition of content in the digital world is changing so quickly.
"There’s a new universe of digital-only brands who need what we do, technology is making ROI and CRM more meaningful and consumers are demanding sense in the midst of a lot of noise.
"These stars all align to create opportunities for an established, skilled and trusted company such as John Brown. I am looking forward to growing our digital footprint as a business, especially via a new digital client base."
Billingsley will report to Libby Kay, the managing director at John Brown.
Andrew Hirsch, the chief executive at John Brown, said: "We approached Rebekah because of her breadth of experience and understanding of publishing brands in the digital space, as well as her new business development and commercial experience."