He will be responsible for facilities management at 29 hospitals, 95 mental health units and 96 primary care centres across the UK, including the University College London Hospitals.
Mr Ridley resigned as chief executive of Salisbury NHS Foundation Trust in September just six months into the £150k-a-year job.
Before joining the NHS he was a deputy vice-president for oil giant Shell and head of public affairs for fertiliser company Syngenta.
Interserve executive director Bruce Melizan said: “Caspar’s appointment reinforces our plans to be able to provide the healthcare sector with a joined-up approach to facilities management and estate provision, and to further our expertise in this sector.”
Mr Ridley said that he was excited to be joining Interserve. “My experience working within the industry, and the current challenges the healthcare sector is facing, means that it is now more important than ever to put the patient at the heart of service delivery,” he said. “I’m looking forward to the task of helping hospitals and other health organisations reduce their operating costs and improve clinical pathways and care.”