Nishimura was born in a farmhouse in Kamata village (today a part of Gose, Nara) to a lumber-dealing father.

[2] Nishimura was hard-working and worked a number of different jobs throughout his youth, such as being a shopkeeper,[3] a hardware dealer for nails,[4] and, after returning to his native Osaka (which was right next to his home village), he became an office assistant at an insurance company.

[5] In 1933, he joined the Sakai city council, where he helped to form a national office worker union which was forcibly dissolved by the government only half a year later.

Under his rather brief tenure as chairman, the DSP's electoral performance was very stable, increasing their popular vote share by only 0.1% and their number of Diet seats by 3 in the 1968 House of Councillors election, and increasing their popular vote share by only 0.3% and gaining a single seat in the 1969 House of Representatives election.

[8] In preparation for the 1971 House of Councillors election, Nishimura called for a coalition between the JSP, Kōmeitō, and DSP, which resulted in only limited cooperation between the parties.