McIntosh, who will be replaced by Nicola Burns, formerly operational effectiveness director at the agency, will also stand down from Eventia's board at the end of the year.
He was one of the key drivers behind UDG Healthcare’s purchase of Procon, Universal CIT and World Events, resulting in the merger of Universal Procon and World Events.
During the last year, McIntosh has been splitting his role at Universal World Events with that of chief executive of Ashfield Japan and president of Pharmexx Northern Europe.
McIntosh said: "It has been an incredibly difficult decision - in fact, one of the most difficult I have ever had to make. I joined Ashfield in 1998 at the very beginning and 15 years later it has more than 4,000 employees.
"The meetings and event business now has over 300 employees and Universal World Events has seen double-digit growth year-on-year since its merger."
He added that he will be taking up the role of chief executive at a new pharmaceutical company. "It is a very exciting opportunity and one which I could ultimately not turn down."
Burns started working with Universal World Events’ sister company In2Focus in 2002, and during the last ten years has held a number of different roles including head of sales operations, head of business services and head of HR and training.
She said: "I am thrilled to take on the Universal World Events helm from Graham, and very much look forward to leading the company into the future."
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