Lapo Elkann, who has been employed by Fiat-owned marques Maserati and Lancia since he was 20, has taken on the post of head of strategic marketing for the Fiat brand.
Elkann will be responsible for developing the direction of the Fiat marque across Europe, although national marketing directors, including UK marketing chief for Fiat Franck Ropert, will continue to report to their managing directors.
It is not clear whether Elkann will oversee Fiat brand communications, on which about £40m is spent in the UK, primarily through Leo Burnett and Arc.
Elkann will report to Gianni Coda, the president of the Fiat business unit that has been at the centre of the group's difficulties. The unit incorporates the Fiat and Lancia brands.
Although Fiat delivered a better-than-expected second-quarter operating loss in August of £17.6m, down from £89.5m a year earlier, the company has been hit by falling sales within the car division.
The company has now embarked on a turnaround plan that Fiat chief executive Giuseppe Morchio has said will enable it to break even in 2005.
The strategy includes the launch of more profitable models, including a revamped Fiat Punto, which in July had taken 110,000 orders. In January, Fiat will relaunch the Panda model in the UK.
Fiat's UK sales for the year to September were 61,135, a fall of 11.2%, compared with a 0.5% rise in the overall new car market, according to the Society of Motor Manufacturers and Traders.
Under a complex deal, 20% of Fiat Auto is owned by General Motors, with an option to sell the remaining 80% to GM from next year. Agnelli, the firm's legendary founder, died of cancer earlier this year.