Pringle was born in New York City. He served in the army during World War I and graduated from Cornell University. He became a reporter for the New York Sun, New York Globe, and New York World. He won notice for his biographical articles, written in a muckraking style. This led to his first book, a 1927 campaign biography of New York Governor and presidential aspirant Al Smith. In 1931 he published Theodore Roosevelt, a Biography, which attempted to debunk some of the former president's more colorful accounts of his own life while providing a detailed portrait of his political career and also his personality. Pringle made full use of the Roosevelt presidential papers on deposit in the Library of Congress, and was clever enough to conceal the fact that he knew little about the final decade of his subject's life. 
In 1939 Pringle published a more sympathetic 2-volume biography of William Howard Taft, The Life and Times of William Howard Taft.
After teaching as a professor at the Columbia School of Journalism from 1932 to 1942, Pringle moved to Washington, D.C. during World War II to head the publications division of the United States Office of War Information. In his later years he wrote magazine articles and book reviews. He also was a member of the Peabody Awards Board of Jurors from 1954 to 1956. Pringle was married twice, to Helena Huntington Smith and to Katherine Douglas, and had two children. He died in Washington, D.C. on April 7, 1958. At the time of his death, he was working on a joint biography of Theodore Roosevelt and Woodrow Wilson, but the unfinished manuscript was never published. His papers are in the Library of Congress.
In 1954 Massachusetts Institute of Technology (MIT) historian John Morton Blum published The Republican Roosevelt, which revived the reputation of Theodore Roosevelt, countering Pringle's portrayal of him as a blustering politician who never grew up that kept him from being taken seriously.