He becomes a non-exec director with immediate effect and takes the reigns as chair at the radiation detection specialist after the AGM next month.
The 70-year-old is currently chairman of the Daiwa Anglo Japanese Foundation, a UK-based charity to support closer links between Britain and Japan, and has been chairman and chief executive of Oxford Instruments (LON:OXIG).
He has advised the UK Government on science and education, conducting a review of primary mathematics in 2008 and in 2010, and was a member of the international review of the Intergovernmental Panel on Climate Change (IPCC) for the UN Secretary General.
Williams said today: "I am pleased to be joining Kromek at this exciting juncture. I feel I can contribute a great deal based on my significant sector experience and, in particular, my time at Oxford Instruments. I am impressed by the management team and the scale of the company's operations."
Lawrence Kinet, Kromek's interim chairman, added: "Over the last six months, we have appointed a new broker, achieved progress in our new commercial markets and completed a successful fundraising, which is supported by our revolving credit facility with HSBC.
"As a result, the company is now in a stronger financial position, and we look forward to leveraging Sir Peter Williams' tremendous expertise and experience as we advance to the next stage of our development."
Kromek shares added 5.88% to 27 pence each.