It is the first time that JWT has appointed a global executive creative director.
Fadel will join the agency in its London office this autumn and report to Matt Eastwood, JWT’s worldwide chief creative officer.
At JWT, Fadel’s first responsibility will be to improve the advertising for Unilever’s Sunsilk brand, but he will expand his brief to work with other clients.
He will also help the agency in pitching for new business.
At Lew’Lara\TBWA for 11 years, Fadel started as a copywriter, eventually becoming the partner and chief creative officer.
Eastwood said: "Manir joins us with the creative pedigree that we are looking for. He makes work that clients love and, importantly, that people connect with."
Fadel added: "As Matt shapes the company’s creative future, I am eager to help him and the network achieve every goal they have set in their creative crosshairs."
His arrival does not affect the reporting structure of the London management team.