He will be succeeding Lynne Regent, who retired in August 2021, after 13 years as chief executive.
Commenting on his appointment, Williams said: "I am really excited to lead a dedicated team at the Anaphylaxis Campaign and to work very closely with the wider community and organisations so there are no more unnecessary deaths and hospitalisations through severe allergic reactions."
He was previously head of external affairs at Heart UK (the cholesterol charity) where he led successful campaigns for better services and access to medicines for people with heart disease.
Williams also played a ‘leading role’ in transforming the charity’s communications, commercial partnerships and income generation.
Sarah Baker, Interim chief executive of the Anaphylaxis Campaign, added: “On behalf of the Board of Trustees and staff, I am delighted to welcome Simon Williams as our new CEO. Simon brings great experience and knowledge and we’re all looking forward to working with him on exciting plans for the next phase of the Campaigns development.”