The globe-hopping executive bridged the cultural and geographical distance between the two groups, easing them closer together and building them into one of the world’s largest carmakers.
The alliance, which since 2016 has included Mitsubishi Motors, has reshaped much of the industry, launching new product segments and pushing into electric cars years ahead of rivals.
The question of whether the partnership can outlast its chief architect has always lingered — and now may soon need to be answered.
Nissan on Monday pledged to remove Mr Ghosn from his position as chairman, following allegations of “serious misconduct” around reporting of his pay, and use of company assets.
Mitsubishi, in which Nissan is the largest shareholder, followed suit several hours later in pledging to remove Mr Ghosn from his chairmanship, while saying it will investigate the issue.
Renault, where Mr Ghosn is both chief executive and chairman, said it would convene a board meeting, expected to be held later this week.
The alliance, which has its own head office and executive staff, did not issue a comment.
As well as chairing Nissan, Mr Ghosn is chief executive and chairman of Renault and chairman of Mitsubishi. He is also chief executive and chairman of the alliance.
Mr Ghosn’s expected departure from Nissan, which is set to be approved by the company’s board on Thursday, comes as the three carmakers seek to deepen their alliance, with aggressive cost-saving targets and plans to co-manufacture most of their vehicles by 2022.
Currently, the carmakers share some procurement, manufacturing and research spending. Combined, it is the second largest car group in the world behind Volkswagen, with sales of more than 10m cars a year.
But investors will be asking whether the development marks “the “Re-Japanisation” of Nissan and the end of the alliance,” said Max Warburton, auto analyst at Bernstein.
Several former senior executives from Nissan or Renault, who spoke on the condition of anonymity, credited Mr Ghosn with being the force that bound the two unlikely members.
“They don’t trust each other,” said one former Renault executive. “They are very different cultures, with long brand histories and lots of pride in them.
“You can only say it’s a huge success because of him.”
Principally, he held the companies together by a gruelling travel schedule, spending at least a week in each headquarters every month during the years he held down both CEO positions, as well as considerable time travelling around the global operations of the companies.
“His mastery of detail is huge,” said one former colleague.
Ghosn, a Lebanese-Brazilian, also displayed something of a cultural dexterity, frequently meeting with everyone from heads of state to factory workers in scores of countries, touching down in his private jet for hours before heading on to the next location.
Yet for Nissan CEO Hiroto Saikawa, and critics of Mr Ghosn’s totemic leadership, his overarching presence was too much.
In an extraordinary press conference in Japan on Monday evening, the Nissan boss, a colleague of Mr Ghosn’s for decades, hit out at his former boss, saying he wielded too much power within the companies he led.
“This is not the only cause but it is one of the factors or drivers [behind the alleged misconduct],” Mr Saikawa said.
“This is the negative aspect of the long regime of Mr Ghosn. This is a fact that we need to admit.”
When asked if Mr Ghosn was a “dictator”, Mr Saikawa paused, before saying he needed more time to consider the question.
Mr Ghosn stepped back from Nissan’s CEO position in early 2017, remaining as chairman and focusing more on the alliance.
Although he had been due to remain as Renault CEO until 2022, he told the FT earlier this year he may leave earlier.
Since leaving the Nissan leadership post, the alliance has appointed more than two dozen managers from either carmaker, creating new joint functions that will oversee a range of areas from manufacturing and quality to customer services and new business ventures.
The goal, according to people close to Mr Ghosn, was to create his own super-company that allowed him to run the global operations while the chief executives of three listed car manufacturers operated beneath him.
This makes finding a replacement, if one is needed at the top level, even more difficult.
There is currently no clear deputy capable of leading the three businesses.
In the past, promising executives operating under him often left before being given the chance to lead, such as PSA’s Carlos Tavares.
Mr Saikawa hinted at the need to reduce reliance on a single leader.
“In the future, we will make sure we don’t rely on specific individuals, rather will look at most sustainable structure, and in this we need to talk to the partners and to revise the way we work,” he said in his press conference.
Yet Nissan’s power over the future of the alliance is limited. Renault, which holds 43 per cent of Nissan’s shares, has the power to appoint Nissan’s chairman, and ultimately has far more control over the whole alliance, according to several people who have worked in the business.
Political issues, such as the French state’s 15 per cent holding in Renault, have always prevented the three companies from seeking a full merger.
But Mr Ghosn has talked openly in the past about creating a structure that is “irreversible”, so that the businesses can continue after he has left.
An analyst at JPMorgan said Mr Ghosn was the “driver” of the alliance, and “investors need to be reassured with regards to the co-operation between Renault and Nissan in light of the recent events as it is critical to Renault’s strategy going forward.”
Mr Saikawa, in his press conference, said he would work with the other companies.
“The partnership among the three entities will not be affected by this event,” he insisted. “We will closely work together with the alliance partners, containing any possible confusion and working together on alliance efforts.”
The French government has also said that the stability of Renault is of paramount importance.
“I think in this type of situation, more than ever, we need to be calm . . . to see what the different options are and to decide after that,” said French finance minister Bruno Le Maire.
Additional reporting by Kana Inagaki and David Keohane
Career of a global car titan
Recruited by Renault’s then CEO Louis Schweitzer from Michelin, where he had worked for 18 years and risen to head the French tyremaker’s US operations.
Dispatched by Schweitzer to sort out Nissan, where he becomes chief operating officer, after Renault formed an alliance with the ailing Japanese carmaker, taking an initial 37 per cent stake
Takes over the top job at Nissan
Returns to Paris to take over as chief executive of Renault and retains same job at Nissan
General Motors rebuffs offer of proposed tie-up with Renault-Nissan
Adds role of chairman of Renault to his other positions
After eight-month stand-off, Nissan reaches compromise with French government, which holds just under 20 per cent stake in Renault, to limit Paris’ ability to interfere in Japanese carmaker
Becomes chairman of Mitsubishi after it joins the alliance following Nissan’s move to take a 34 per cent stake in its scandal-hit Japanese rival, which was embroiled in an emissions testing scandal
Relinquishes chief executive role at Nissan after 16 years to Hiroto Saikawa but remains chairman
Re-appointed chief executive of Renault for a further four years but admits in June he expects to step down before his term is out