Masuko joined Mitsubishi Motors in 2004 and became president in 2007. He oversaw the creation of the partnership between Mitsubishi and Nissan.
Mitsubishi Motors said he died on Aug. 27.
Masuko was at the helm of Mitsubishi during a 2016 scandal in which the automaker was found to have overstated the mileage on its vehicles. An investigation uncovered slack governance and pressure on resource-starved engineers as chronic issues at the company.
The deal was agreed between Masuko and then Nissan CEO Ghosn, and brought Mitsubishi in as a junior partner in the Nissan-Renault automotive alliance.
Masuko later denounced his ties with Ghosn following the latter's 2018 arrest in Japan over suspected financial misconduct.
All three members of the alliance currently are mired in financial problems, after years of aggressive expansion policies under Ghosn's leadership.