Ross will take over the role from current chair Ed Warner and will start the position on 1 April, 2021.
Warner is leaving the firm after having served the maximum term possible in accordance with the firm’s membership agreement.
The appointment follows the firm finalising its 2020 trading results, expecting to show stable like-for-like revenue and an increase in underlying profitability to 2019 performance, despite the issues resulting from Covid-19.
Dave Dunckley, chief executive at Grant Thornton UK LLP, said: “We very much would like to thank Ed for his service both as an independent non-executive and board chair over the past 10 years and welcome Imogen’s appointment.
“She will undoubtedly provide us with the same high levels of diligence, challenge and support as Ed has over the years, whilst also bringing her own perspective and experience to the role.”
Ross said: “The past four years on Grant Thornton’s Board have given me a unique insight into the firm’s distinct culture and values, which I believe truly sets it apart from its peers.
“I’m delighted to be taking on the role of Chair and working with the firm as it continues to go from strength to strength.”