He oversaw the transformation of the WMA from the Association of Private Client Investment Managers and Stockbrokers and has played a leading role in establishing the organisation as the primary voice of the UK's wealth management sector during his tenure.
Mr May will begin his handover to Liz Field on 1 September.
Ms Field was previously chief executive of the Financial and Legal Skills Partnership and brings extensive experience of wealth management and the wider financial sector.
She was previously CEO of the Financial Services National Training Organisation, the Banks and Building Societies National Training Organisation, and the Insurance Industry Training Council.
{desktop}{/desktop}{mobile}{/mobile}
Wealth Management Association chairman Tim Ingram said: "Tim has done a fantastic job leading the WMA over the last four years, taking the organisation through a period of significant change, and we are sorry that he has decided to step down.
"The significant increase in recent times in the membership and profile of the WMA is a clear tribute to his achievement. We wish him the very best in his future endeavours.
"We are delighted to have secured someone of Liz Field's calibre.
"Liz brings many years of experience in leading trade organisations, championing the work of sectors in the financial services area, together with a good knowledge of wealth management having worked at Gerrard. I am sure she will further enhance the WMA's position as the leading voice of the wealth management sector."
Mr May said: "I'm proud of the WMA's achievements on behalf of our community of firms and their 4 million clients.
"After four years of endeavour, backed by a great team of staff, I'm looking forward to assisting Liz up to our Annual Conference on 6 October 2014.
"I wish her and the community well for the future."
Ms Field said: "I am delighted to be joining the WMA at such an important time. Businesses operating in the wealth management sector are facing many challenges both in the UK and in the international market place.
"I am excited about helping the WMA membership to navigate through the many changes and challenges they are facing and to support in promoting the sector. The wealth management industry makes an important and very valuable contribution to the British economy, and I look forward to working with the Board and the WMA team to help drive sustainable growth."