French automaker Renault and Japanese partner Nissan officially launched their "rebalanced" alliance on Wednesday after the overhaul was approved by regulators.
The companies announced an agreement in February to reboot a quarter-century-old partnership that has been marred by tensions in more recent years.
A part of the deal, Renault reduced its stake in the Japanese automaker from 43.4 percent to 15 percent, the same size as Nissan's share in its French counterpart.
Nissan agreed to take a stake in Renault's new electric vehicle venture, Ampere.
"After having obtained all required regulatory approvals, the New Alliance Agreement between Renault Group and Nissan comes today into force," the companies said in a joint statement.
The alliance began in 1999, when Renault rescued Nissan from bankruptcy. Mitsubishi Motors joined in 2016, when Nissan took a 34-percent stake in its struggling Japanese rival.
Tensions erupted in 2015 when the French state increased its stake in Renault. This was later reduced and an agreement was reached to cap the government's ability to interfere in the alliance's affairs.
The union was shaken again by the 2018 arrest of Nissan boss Carlos Ghosn, who claimed the charges against him were intended to prevent him from bringing the Japanese and French automakers closer together.
Renault chief executive Luca de Meo said in Wednesday's statement that the companies were "now effectively entering this new era of the Alliance with a pragmatic and business-oriented approach".
Nissa CEO Makoto Uchida said: "Based on this equal footing, Nissan will continue to harness our core competencies and be more agile to explore further growth opportunities that support our business strategy".