McCartney, who has worked at the hand made cosmetics retailer for the past 13 years, was responsible for its news-based publication, Lush Times, which is sent out quarterly to around 1m subscribers.
During her time at Lush, the family owned ethical retailer has gone from a four store property in the UK to operating over 700 stores in 43 countries, still manufacturing its own products by hand. She was also responsible for brand building efforts in the UK, as well as the retailer's customer magazine, called Scent.
McCartney is a regular speaker on ethical business issues, such as the approach to reducing packaging, preservatives, waste and energy use.
She said that she would be taking time out for family reasons and also to begin work on a business book of ethics.
McCartney will leave in April and the comapny has no plans to replace her directly.