By Eric Sylvers in Milan and Nora Naughton in Detroit and Ben Dummett in London

MILAN--Fiat Chrysler Chief Executive Mike Manley will become head of the Americas following the Italian-American company's merger with France's PSA Group, ensuring the new group can leverage the veteran executive's experience.

Mr. Manley has worked for Fiat Chrysler and its former incarnations for two decades. He has deep knowledge of the U.S. market where he headed up the Jeep brand, which he helped elevate to new highs in profitability and vehicles sold. Mr. Manley became Fiat Chrysler's CEO in July 2018 in the wake of the sudden sickness and death of Sergio Marchionne.

"Mike took the helm of our company under the most difficult of circumstances, with Sergio's cruel and premature passing...and he took us out of those dark days, leading by example," Fiat Chrysler Chairman John Elkann wrote in a letter to employees on Friday announcing the move.

Mr. Elkann, the great-great-grandson of Fiat founder Giovanni Agnelli, will be chairman of the newly merged company, to be called Stellantis.

PSA CEO Carlos Tavares will hold the same position at Stellantis, which will be one of the world's largest car companies following the merger that is slated to close by the end of March. Fiat Chrysler and PSA--which makes the Peugeot and Citroen brands--sold 8.7 million vehicles between them last year, more than General Motors Co.

The 56-year-old Mr. Manley played a central role in negotiating the merger, the auto industry's biggest tie-up since 1998, and his experience with the U.S. market was considered key to making the combination a success, some bankers have said.

The Brit has long been a fixture in Fiat Chrysler's executive ranks and has served as the head of the Jeep and Ram brands, which churn out the bulk of their profit in North America. Fiat Chrysler's North American operations have been the group's cash cow for years, offsetting losses racked up in other parts of the world.

That experience in North America will be fundamental for Mr. Tavares. The Portuguese executive successfully turned around the Peugeot brand and the European business of General Motors Co., which PSA bought in 2017, but he has limited experience in the U.S.

PSA doesn't sell cars in the country, but has announced plans to reintroduce the Peugeot brand there after an almost 30-year hiatus.

But Mr. Manley has struggled to fix the company's faltering business in Asia, where Fiat Chrysler is still a marginal player in China. The company's plans to radically increase Jeep's market share have fizzled. Europe has long been a dark spot for Fiat Chrysler and Mr. Manley hasn't managed to engineer a turnaround in the group's second-biggest market during his two and a half years at the helm, a tenure that has been marked by the coronavirus pandemic.

When the Covid-19 crisis spread globally earlier this year, Mr. Manley steered Fiat Chrysler through unprecedented, extended plant shutdowns across the globe and the company moved quickly to shore up its cash, cutting the dividend.

Mr. Manley had said on several occasions, including in September at an event for Fiat Chrysler's Maserati brand, that he intended to stay on following the merger. That did little to quash speculation that after being spurned for the top job that he would leave Fiat Chrysler to head up another car maker.

Write to Eric Sylvers at eric.sylvers@wsj.com, Nora Naughton at nora.naughton@wsj.com and Ben Dummett at ben.dummett@wsj.com

(END) Dow Jones Newswires

12-18-20 1012ET