Andrew Rooney was born in Albany, New York, the son of Walter Scott Rooney (1888–1959) and Ellinor (Reynolds) Rooney (1886–1980). He attended The Albany Academy, and later attended Colgate University in Hamilton in Central New York, where he was initiated into the Sigma Chi fraternity, until he was drafted into the United States Army in August 1941. Rooney began his career in newspapers while in the Army when, in 1942, he began writing for Stars and Stripes in London during World War II.
In February 1943, flying with the Eighth Air Force, he was one of six correspondents who flew on the second American bombing raid over Germany. Later, he was one of the first American journalists to visit the Nazi concentration camps near the end of World War II, and one of the first to write about them. During a segment on Tom Brokaw's The Greatest Generation, Rooney confessed that he had been opposed to World War II because he was a pacifist. He recounted that what he saw in those concentration camps made him ashamed that he had opposed the war and permanently changed his opinions about whether "just wars" exist.
In London, during the war, Mary Hemingway made an accusation of plagiarism against several fellow journalists, including Andy Rooney, although the accusations were proven false.
