During World War II, Kenny was an active proponent of the incarceration of Japanese Americans, which the California Attorney General's office has since apologized for, describing it as a "failure of political leadership" and a racist policy.

His father, Robert Wolfenden Kenny (1863-1914) was a successful banker and civic leader in Los Angeles and Berkeley, California.

[2][3] In 1921, Kenny joined the Los Angeles Times, where he worked with Chapin Hall, and eventually became a financial editor there.

Although Warren was a Republican, California law at that time permitted a candidate to run in both primaries, a practice known as cross-filing.

[3][5] In 1937, Kenny supported Franklin Delano Roosevelt's battle to "pack" the United States Supreme Court with extra justices via the Judicial Procedures Reform Bill of 1937.

[2] As The New York Times wrote in Kenny's obituary: "Out of that battle grew the National Lawyers Guild" (NLG).

[7][8] In May 1945, while serving as Attorney General, Kenny accompanied Bartley Crum and Martin Popper to the founding session of the United Nations in San Francisco, where the three men were NLG's "official" consultants to the American delegation at the behest of the U.S. Department of State.

[2] In 1947, NLG members Charles Katz[9] and Ben Margolis[10][11] asked Kenny to become lead counsel, with Crum as his second,[12] for the "Unfriendly Nineteen" film industry professionals subpoenaed to testify before the House Un-American Activities Committee (HUAC).

Later, NLG members Martin Popper of Washington and constitutional lawyer Sam Rosenwein of New York also joined the legal team.

In her review of Janet Stevenson's 1981 biography of Kenny, The Undiminished Man, Dorothy Gray writes:Until Bob Kenny chose to oppose the outrages of the McCarthy era, it appeared as though he would achieve a high political office or gain appointment to the California Supreme Court.

When, in the late 1940's, he chose to defend those accused of being pro-communist, he sacrificed all hope of high office and became a political untouchable.

Partner Robert S. Morris was a member of the Immigration and Deportation Committee in the Los Angeles chapter of the American Civil Liberties Union (ACLU).

[15][16] In 1962, Kenny served as counsel of Albert J. Lewis and Steve Roberts of the Fair Play for Cuba Committee before HUAC.

[17] In 1963, the Congressional Record re-recorded information from October 26, 1955, that "public records, files, and publications of this committee" (HUAC) showed Kenny "not necessarily a Communist, a Communist sympathizer, or a fellow traveller" but noted nevertheless that he was affiliated with the American Youth for Democracy, Civil Rights Congress, Joint Anti-Fascist Refugee Committee, and California Labor School.

"[2] Robert Walter Kenny died age 74 on July 20, 1976, at Scripps Memorial Hospital in La Jolla, California with no survivors.