Clark had served as chief executive of Unlimited’s Communication division since September 2019, following 21 years as managing director of Nelson Bostock.
Hart steps up from his role as managing director of Nelson Bostock to oversee the growth and direction of an agency portfolio that also includes Fever and Health Unlimited.
He will assume the title of Unlimited Communications Group MD rather than chief executive.
In 2020, Hart led Nelson Bostock on a strategic business drive focused on the tech sector. The agency's revenue increased by 29 per cent – a faster rise than any of the other top 10 tech PR firms in the UK, according to PRWeek’s Top 150 Consultancies report.
"Nelson Bostock’s focus on tech has enabled us to support our clients through a period of rapid evolution due to COVID-19. PR and comms have been elevated during the pandemic and have shifted to become the starting point for many integrated marketing models; the creative powerhouse and guardians of brand reputation,” Hart said.
“As a combined force, Nelson Bostock, Fever and Health Unlimited are working together to deliver an excitingly powerful mix of planning, creativity, expertise and campaign delivery. We now offer an unmatched blend of skills and deep experience within the technology, healthcare and consumer sectors.”
Unlimited CEO Tim Hassett said: "Over his 12 years of service at Unlimited, Will has been an inspirational team leader and a grounded, strategic consultant to our clients, making him the natural choice for this role. The opportunity this year is to draw on the strength of specialisms within the teams and our Human Understanding Lab to deliver extraordinary, insight-led work for our clients."
Unlimited Communications said it plans to invest in delivering new services while focusing on its behavioural-led data and insights capabilities to inform creative thinking and campaigns.