Cumnor House, based in Haywards Heath, will welcome Fergus Llewellyn alongside his wife, Tamsyn, and their three children.
He said: “Tamsyn and I are very excited about the prospect of building on the hugely successful Cumnor ethos, outstanding all-round education and community, whilst ensuring that Cumnor pupils are prepared for the challenges of 2020s and beyond.
“We are delighted to be at the centre of its exciting future”.
Fergus has been the headteacher of St Andrew’s School in Turi, Kenya since August 2o15, and prior to that taught at Cheltenham College.
He was at Cheltenham College for 10 years, serving as housemaster and head of English and Drama.
Earlier in his career, he was at Kings Bruton and Haslemere Preparatory School.
Fergus attended the Sherborne School, and graduated from the University of London with a BA (Hons) in English.
James Tanner, chairman of the board of governors for Cumnor House Sussex, said:
“I’m delighted we have such an inspiring headmaster to lead Cumnor on the next stage of its journey.
“In Fergus the board has found an educational professional remarkably well armed to further build the Cumnor community”.
Fergus will be taking over from Christian Heinrich and his wife, Belinda, who spent 19 years at the school as headteacher and wife.
James said: “The board of governors would like to take this opportunity to thank the Heinrichs for the outstanding contribution they have made over the past 19 years.
“Christian and Belinda will leave a remarkable legacy upon which Cumnor House Sussex can continue to grow and prosper.
Cumnor House Sussex is an independent co-educational day and boarding school for two to 13-year-old children.
The school comprises Cumnor Nursery, Cumnor Pre-Prep and Cumnor Prep.
An open day will be held at the school on Friday, September 25 from 10am to 12pm.
Following coffee and a welcome from Fergus, pupils will take parents and prospective students on a tour of the school and answer any questions.
A spokesman for the school said: “There is no better way to learn about Cumnor than to speak directly with our children.
“Each tour can be tailored to your and your child’s interests and admission point.
“We very much look forward to welcoming you to Cumnor, however if for any reason the open day does not go ahead, we will run this event virtually.
To find out more, visit www.cumnor.co.uk.