He was Minister of Internal Affairs and Communications from August 2007 to September 2008, and has served as the president and CEO of Japan Post Holdings since January 2020.

Masuda implemented a nationwide public relations campaign starting in 2001 that branded Iwate as a slower, "no effort" lifestyle alternative to Tokyo and other major cities.

[9] Political and corporate leaders in Japan were jolted by the conclusions of a 2014 book by Masuda called Local Extinctions, a detailed report of population changes that used the latest official figures from the National Institution of Population and Social Security Research to show that 896 cities, towns and villages throughout Japan were facing extinction by 2040.

At first glance, the book simply repeated what earlier reports had concluded; however, it also included the percentages by which child-bearing women between the ages of 20 and 40 were expected to decline in each and every city, town and village.

[12] Masuda was appointed as President and CEO of Japan Post Holdings in January 2020 in the wake of a scandal related to improper sales of insurance products.