The move coincides with a review and re-structure of the Royal Horticultural Society (RHS), during which two sales-focused roles, publisher and head of commercial operations, were merged.
The new role of head of sales will be taken up by Fergus Wilson, who was previously in charge of RHS media sales.
"The RHH has meant a great deal to me - it is a wonderful venue and a great team - but the time is right for me to move on. I am looking forward to a new role within the event industry and maintaining my contacts with the many friends and colleagues I have in the business," said Lyons.
Dan Wolfe, RHS director of members, art and media, added: "For over 15 years Maugie has played a key part in the Royal Horticultural Halls & Conference Centre team, generating millions of pounds of income for the RHS. The RHS would like to thank Maugie for all she has done to support the Society and wishes her the very best for the future."
The restructure affected eight management posts from the Society's 751-strong workforce.
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