Lawson who joined the AEO in October 2006 has decided to purse a freelance career outside of association activity.
In her time as director Lawson has spearheaded the development of key association peer interest groups that focus on specific elements of the AEO community, including international, association and owner manager member companies.
AEO chair Philip Soar said: "I'm very upset that Hilary Lawson has decided to leave us. Her contribution over a difficult two-year period has been enormous, in particular everything she has done to put on the conference and awards last year. It will be difficult to replace her."
The AEO is now set to conduct a recruitment process to replace Lawson.