When Japanese police officers surrounded Carlos Ghosn’s Gulfstream jet last November and packed him off to a Tokyo jail, they unwittingly provoked a seismic realignment of the global auto industry.

Mr. Ghosn’s sudden fall set off a chain of events that, this month, prompted Renault’s chairman, Jean-Dominique Senard, and John Elkann, the Fiat Chrysler chairman, to jump on their mobile phones and entertain a crazy idea: a deal to create the world’s third-largest automaker, according to two people with knowledge of the discussions. After a flurry of phone calls and meetings between the two men over several weeks, Fiat Chrysler formally asked Renault to merge on Monday.

If the deal goes forward, the combined Renault and Fiat Chrysler would elbow past General Motors in car sales and create a new challenger to Volkswagen and Toyota, the global leaders. And if Fiat Chrysler and Renault can patch up strained relations with Nissan, with which the French company has a formal alliance, the three would be de facto the biggest car manufacturer in the world by a wide margin and might force other large automakers to rethink their strategies.

Whether this industry-changing behemoth ever takes shape, though, may depend on what was likely to be a tense meeting Tuesday, which will continue on Wednesday, in Tokyo between Mr. Senard and Hiroto Saikawa, the Nissan chief executive.