PSA – which owns the Peugeot, Citroen and DS brands – agreed in early March to pay around 1.3 billion euros for Opel, a German firm owned by the US automaker General Motors for decades, as well its British subsidiary Vauxhall.
Initially, the deal was to close by the end of the year.
“Groupe PSA today announces the closing of the acquisition of GM subsidiaries Opel and Vauxhall,” the French company said in a statement.
Opel and Vauxhall now have 100 days to draw up a strategic plan which builds on expected synergies of around 1.7 billion euros per year for the new group, PSA said.
Despite remaining a familiar sight on German roads, Opel, the carmaker with the lightning logo, and its British sibling Vauxhall have not registered a profit since 1999.
Based in Ruesselsheim outside Frankfurt, the company was Germany's largest carmaker for decades before losing the crown to Volkswagen.
Last month, the EU approved the merger, saying the combined market shares of the two companies were relatively small in all the bloc’s national markets, only exceeding 40 per cent in Estonia and Portugal.
Opel and Vauxhall employ some 35,600 workers between them at 10 factories across Europe, around half of them at three plants in Germany.
Experts agree that Opel has not matched the success of other manufacturers like Ford or PSA in reducing overcapacity.