Sarah Finch-Crisp has led the trust since 2008 three years after it was formed by English Heritage and the London Borough of Hounslow to oversee the restoration, management and protection of the site. She oversaw a Heritage Lottery Funded £12.1m project to restore the gardens, completed in 2010.
The trust is now actively recruiting for a new director at a salary of between £55,000 and £65,000 with plans to draw up a shortlist by the end of the month and interview in August. The organisation would like the new director to be in post before Finch-Crisp leaves in December.
Chairman Andrew Fane said: "Sarah has done a wonderful job for this unique heritage site since she joined us in 2008 as our first director. She has established an inspiring team to improve and manage the site including its gardens, landscape and buildings.
She has worked constructively with our partners - English Heritage, the London Borough of Hounslow, Chiswick House Friends and others to deliver an organisation which we aspired to in our Heritage Lottery Fund bid of 2005 and the major restoration which concluded in 2010.
"Now we are seeking someone to move us forward to the next stage."
Chiswick House is a neo-Palladian villa built by the third Earl of Burlington in 1729 and set in historic gardens in west London. They are the birthplace of the English Landscape Movement in the 18th century and have inspired countless gardens including New York's Central Park.
As well as looking after the house and gardens the new director will oversee a team which manages education, volunteering, community and special events, security and visitor services.
Fane said that Finch-Crisp had overseen the development of sustainable income streams through commercial activities, including a catering and hospitality business which allowed for reinvestment in the site.
She said: "It has been a privilege to lead the Trust through its first years and a pleasure to work with such enthusiastic, talented and dedicated colleagues and supporters.
"Chiswick House and Gardens are a national treasure and I look forward to seeing them go from strength to strength in the years ahead."
The application deadline is 31 July. See www.chgt.org.uk for more information.