A respected consultant radiologist for more than 17 years, Prof Kay moved into full-time NHS management in 2015.
He has been chief executive of King's since April 2019 and led the organisation throughout the Covid-19 pandemic.
During his time at King's, Prof Kay held the role of lead chief executive for the South East London Acute Provider Collaborative until last year, and is currently chair of the Shelford Group, a collaboration between 10 of the largest teaching and research NHS trusts in England.
Sir David Behan said: "On behalf of the entire Board, I would like to thank Clive for his outstanding leadership, and extraordinary commitment to King's, our people, and the communities we serve. He is a true champion of King's, and the NHS.
"Clive has led King's through an incredibly difficult and challenging period, but his vision and leadership, and compassion for people, has enabled the organisation to come out stronger, more ambitious, and better equipped to tackle the opportunities and challenges we will face going forward."
Professor Kay said: 'It has been one of the greatest honours of my career to lead this superb organisation, and to work alongside the most committed, dedicated colleagues, who do their very best for patients every day.
'King's is important to local people, but also has a truly international reputation, with people from all over the world choosing to build and develop their careers with us. This has motivated and inspired me every day in my role as chief executive.
'I also feel incredibly lucky to have worked in the NHS for so long. The NHS positively impacts so many people every single day, so to be just a small part of this extraordinary institution is something I will always cherish.'
Prof Kay will remain in post until a successor is appointed.
