Opel's supervisory board named Reilly, already head of General Motors Europe, to the post, making him "responsible for all Opel/Vauxhall activities worldwide," a statement said.
Reilly, from Britain, has already begun drawing up a tough restructuring plan for Opel that includes 8,300 job cuts and could cost European governments up to €2.7 billion ($3.9 billion) in state aid. He replaces Hans Demant, who gave up the CEO post to become a GM vice president in charge of global intellectual property rights, the statement added.
In December, US parent GM began to replace directors at Opel after deciding not to sell the European division. It previously named GM financial director Walter Borst as head of Opel's supervisory board.
Opel also named Mark James, another Briton, as its new chief financial officer. Like Reilly, who has worked at GM for 35 years, James has experience with GM brands in Asia, having worked at the Korean operation Daewoo.
Rita Forst, from Opel's technical development centre in Rüsselsheim, west
Germany, was named head of engineering. The new board "will address our tasks quickly and with plenty of energy," Reilly said in the statement.
"We in particular will be on the offensive and will want to increase our market share in Europe," he added.
Opel nonetheless said Friday that around 12,000 of its workers in Germany, roughly half its domestic workforce, will work fewer hours in January and February owing to slumping sales.
One of Reilly's first tasks will be to convince Opel's works council, on which sit union officials, to accept the permanent job cuts which it rejected in late December.