Neil Clitheroe (pictured) joins as MD from renewable energy giant Iberdrola, where he was CEO of its UK competitive business at ScottishPower, as well as global retail director for Iberdrola across five international markets.
ScottishPower has been a Stonehaven client since the comms agency was founded in 2014 by former Lynton Crosby associate Peter Lyburn.
In addition, former Teneo deputy head of UK public affairs India Knight has joined the agency as a director.
Stonehaven said the appointments follow a run of significant client wins in 2019, including Visa, National Grid and Barclays. The agency also boasted a fifth successive year of double-digit growth, with revenue set to reach £5.1m this year and work to be spread across a team of 30 full-time consultants.
Clitheroe said: "I’m joining because Stonehaven offers one of the most compelling, data-driven approaches I have seen in a management consultancy. Thanks to Stonehaven’s evidence and advice, ScottishPower became much bolder on owning decarbonisation, setting the business up to play a strong role at COP26.
"I’m thrilled to help grow the team and help our clients respond to the generational challenges facing today’s business leaders. Campaigning and public policy responses to decarbonisation, market regulation and political shifts are all well understood at Stonehaven. I am excited to get going."
Lyburn said: "The expertise of Neil and India bring even more firepower, experience and expertise to an exceptional team. Neil has lived first-hand the challenge of reforming a major business under the political spotlight. This experience is valuable as decarbonisation, ESG and market reform pressures are touching all our clients."
Former Portland partner Thornton is to leave Stonehaven after two years.
Lyburn said: "Ben has helped lead us through this important phase as a business and I wish him the very best for the exciting next chapter of his story."
Stonehaven's senior team also includes Caroline Preston, former head of broadcasting at Number 10 under David Cameron's Premiership.