Dr Findlay has been in charge since June 2022 and was previously deputy chief executive and chief medical officer of UHSussex's predecessor organisations, Western Sussex Hospitals NHS Foundation Trust and Brighton and Sussex University Hospitals NHS Trust.
He will begin a practical handover of his duties from mid-July.
Dr Findlay said: 'Our new strategy for 2025-30 is a major, important piece of work for everyone in our Trust and everyone who uses our services. It's designed to unlock our potential as one of the largest NHS organisations in the country and will deliver millions of pounds of investment into buildings, services and helping colleagues develop their skills.
'There's every reason to be confident our hospitals have a great future, but the strategy for realising it needs to be led by someone who will see it through to 2030 and beyond.'
He added: 'I've worked in the trust for more than 10 years and am very proud to have been its chief executive for the last three. However, leading such a large, diverse organisation is a hugely demanding job and I do not anticipate continuing to do so for a further five years. That means this is the right moment to make a change, and so I will be stepping down as chief executive.'
UHSussex Chair Philippa Slinger said: 'I would like to thank George for his service to the Trust and its predecessor organisations. He has overseen an impressive range of improvements, and I would like to wish him well for the future.
'Our new strategy will set out how we intend to go further again and ensure patients get faster access to excellent care across all our hospitals. We will now seek a new leader for the new era ahead.'