Mike Masaru Masaoka was born in Fresno, California, in 1915, the fourth of eight children of immigrant parents. A few years after his birth, his father moved the Masaoka family to Salt Lake City. It was there that he earned the nickname "Mike" while attending Salt Lake City schools. Later, he had his name legally changed. After graduating from West High School, he attended the University of Utah while working in his family's produce business and local restaurants. At both West and the University, he excelled in forensics. He was graduated from the University in 1937, after studying economics and political science.

Masaoka's first involvement with the Japanese American Citizens League (JACL) occurred in 1938, when he attended an annual gathering of the organization. He became interested in the group's goal of organizing second-generation Japanese Americans, or Nisei, in efforts to counteract increasing discrimination. Masaoka quickly became a leader in the JACL after organizing the Intermountain District Council in Utah and Idaho. At the outbreak of the Second World War, the JACL's role as the leading representative organization for the Nisei took on new significance when coping with the government's decision to evacuate and intern all West Coast noncitizens and Americans of Japanese ancestry. As the JACL National Secretary, Masaoka was sent to Washington, D.C. in an effort to mitigate the effects of forced removal and work towards the elimination of the internment camps. Before leaving for Washington, though, Masaoka wed Etsu Mineta.

In addition to exerting influence on the United States government concerning the situation of Japanese Americans, while in Washington Masaoka also worked towards the reinstatement of military service for Japanese Americans. His efforts resulted in the formation of the 442nd Regimental Combat Team. Masaoka, along with his four brothers and many other Japanese American men, joined the 442nd, which served with honor in military campaigns in Italy and France.

After returning from military service, the JACL appointed Masaoka as its Washington Representative, a post at which he served full-time until 1952, and part-time until 1972. During his years as a lobbyist, Masaoka worked to reform immigration and naturalization laws, resulting in the repeal of the 1924 Japanese Exclusion Act and the abolishment of the National Origins Quota Immigration System. In addition, he lobbied for reparations for losses suffered by Japanese Americans who had been relocated to the internment camps, which assisted in passage of the Evacuation Claims Act of 1948. In the 1980s, he also played a role in the proceedings of the Commission on Wartime Relocation and Internment of Civilians, which investigated the topic of further redress. Throughout his years in Washington, Masaoka also supported passage of civil rights legislation, and was active in development of smooth Japan-U.S. diplomatic and economic relations. In addition to his lobbying efforts on behalf of the JACL, in 1953 Masaoka established his own consulting firm, Mike Masaoka Associates. His clients included both American and Japanese manufacturing firms, as well as a variety of trade associations.

Masaoka was involved in a variety of Nisei veterans associations, including the "Go For Broke" National Veterans Association. He was the first Nisei elected President of the Japan-America Society, a group with which he maintained a long association. In 1970, the Mike Masaoka Distinguished Public Service Award was established by the JACL as a way to recognize individuals who had made significant contributions to the well-being of the Japanese American community. He was the JACL "Nisei of the Biennium" in 1950, and the JACL has established the Mike M. Masaoka Fellowship Fund to develop leaders in public service at the national level. In 1968, Masaoka was awarded the Third Order of the Rising Sun by the Emperor of Japan. In 1983, he was honored with the Second Class Order of the Sacred Treasure by the Emperor.

Masaoka's autobiography, They Call Me Moses Masaoka (written with Bill Hosokawa), was published by Morrow in 1987. He died in Washington, D.C., in 1991, after being plagued with heart problems during the previous decade. He was preceded in death by his two adopted children, and survived by his wife and one grandchild.