Mr Strang will continue to lead the organisation until a new chief is appointed.
He said: “It has been a privilege to work with so many talented and enthusiastic people and I wish my colleagues and the organisation continued success in the years to come.
“I would also like to thank the board for their support and guidance over the years.”
During his time as chief executive, customer visits have doubled, and the charity now operates many more services and facilities on behalf of West Lothian Council.
Mr Strang also led the successful negotiations as chair of Community Leisure Scotland with the Government to stop the removal of rates relief from charitable trusts as part of the Barclay Review.
More recently, Mr Strang has been instrumental in developing a three-year plan that will address rising costs and significant funding cuts.
He has agreed, at the board’s request, to remain with the organisation while the initial stages of this plan are implemented, having already completed a restructure of the management team.
Dr Cindy Brook, chair of West Lothian Leisure, said: “I appreciate the leadership that Robin has given to the company and for developing it into an organisation that has improved the health and wellbeing of so many people in West Lothian.”
The recruitment process to replace Mr Strang will get underway in the near future.