Shelbourne has run the agency's creative department for almost nine years.
His new international role will see him become one of ten worldwide creative directors, working on some of the network's key global accounts. However, it is as yet unclear which pieces of business Shelbourne - who joined the agency from working on an oil rig in the North Sea in 1983 - will work on.
The agency has yet to line up a successor to head the UK creative department, but it is unlikely to involve anyone currently working there.
Simon Bolton, the chief executive of JWT London, is in discussions with a number of external candidates, but a decision has not yet been made.
However, an appointment is expected by the end of January next year, with Shelbourne set to take up his new role a month later.
In his international position, Shelbourne will be working closely with the European creative director, Gordon Torr, and the network's global business directors. He will report to the JWT president and chief executive EMEA, Michael Maedel.
Shelbourne said: "I've thoroughly enjoyed every day of my long tenure. I'm very proud of the reel and department I leave behind, and very much look forward to my future role."
Bolton added: "We are delighted that Jaspar has been given this opportunity to develop his talents and experience on an international stage. We wish him all the best in his new role."