Born in Lake Placid, New York on September 26, 1893, as the Progressive Era was getting under way, Kirchwey was the daughter of pacifist Columbia Law Professor George Kirchwey. She attended Barnard College from 1911 to 1915, working locally in journalism after graduation, at the New York Morning Telegraph, Every Week magazine, and the New York Tribune.
In 1918, she was brought to The Nation by then editor Oswald Garrison Villard, largely at the behest of Kirchwey's former professor at Barnard, Henry Raymond Mussey, first working in the International Relations Section. In 1922 she became managing editor and published a collection of articles, dealing primarily with changing sexual relations, in 1925 entitled Our Changing Morality . She succeeded Villard as editor of the magazine in 1933, first as part of a four-person committee, then as the sole editor, becoming the first woman at the top of the masthead of a national weekly newsmagazine. In 1937, she bought the magazine from Maurice Wertheim, who had purchased it from Villard in a brief and particularly contentious period of the magazine's history.
As editor, Kirchwey was strongly supportive of Franklin Delano Roosevelt's New Deal and later broke with Villard in her support of Roosevelt's involvement in World War II. She was strongly supportive of the anti-Franco faction during the Spanish Civil War and supported the creation of an independent Jewish state. Her opposition to fascism led to a strong belief in the value of strong ties to the Soviet Union, opposing fascism in general and Nazism more specifically. On the domestic front, she was a sharp critic of the House Un-American Activities Committee -- calling Martin Dies, its leader from 1938 to 1944, a "one-man Gestapo from Texas" -- and the growth of McCarthyism in America. As a result of this evolution in the magazine's politics, both The Nation and its editor were criticized strongly, even at times by members of the American left; Arthur Schlesinger, Jr. famously referred to the magazine's "wretched apologies for Soviet despotism."
The magazine's political marginalization, however, also had financial consequences, becoming a significant financial drain by the early 1940s. As a result, Kirchwey sold her individual ownership of the magazine, creating a nonprofit organization, Nation Associates, formed out of the money generated from a recruiting drive of sponsors. The organization, also responsible for more the academic responsibilities, including conducting research and organizing conferences, that had been a part of its early history, became responsible for the operation and publication of the magazine on a nonprofit basis. Kirchwey, as president of Nation Associates, remained editor of the paper until 1955, when Carey McWilliams became editor and George Kirstein became publisher.
After 1955, Kirchwey became involved with a collection of civil rights and pacifist organizations, most notably the National Association for the Advancement of Colored People. She died on January 3, 1976, in St. Petersburg, Florida.