Stephenson is one of the most influential modern car designers and is responsible for designing cars like the new Mini and X5 during his tenure with BMW, along with Maserati's Quattroporte and MC12 sports car.
During his time at Fiat, the design centre has created models like the Grande Punto, Bravo and the new 500, which sparked a dramatic turnaround in the company's fortunes.
Since joining Centro Stile, Stephenson was responsible for the design of the new Mi.To hatchback and prompted development of the 149 hatchback and 169 executive sedan.
Stephenson will be replaced at Alfa by Christopher Rietz.