Born in N.Y.C., 1901, Rainger taught himself music composition and theory while still in high school. He received a scholarship to a music school, but quit after one year to adhere to his father's wishes and attend law school. While working as a lawyer, Rainger spent his nights playing piano in a dance orchestra, until turning back to music full-time in 1926. He was in a duo with Edgar Fairchild for a few Broadway musicals, before the two co-led an orchestra in the 1928 production, Cross My Heart. He also performed in a piano duo with Adam Carroll in 1929's The Little Show, which included Rainger's first hit song, "Moanin' Low." He worked as accompanist and arranger for various vaudeville acts and vocalists, until moving out to Hollywood in 1932 with lyricist and songwriting partner Leo Robin. Before this move, the duo already had hits with "Louise," "I Have to Have You" (1929) and Fanny Brice's "torch" song, "When a Woman Loves a Man" (1930), among others.

Rainger and Robin worked for Paramount Pictures from 1932 until 1938, and became the leading film songwriting duo of the '30s and early '40s, with over 50 hits. Some of Rainger's best-known songs include "Please" (1932), "Love in Bloom" (1934), "With Every Breath I Take," "If I Should Lose You" (1935), "Blue Hawaii" (1937), and "Thanks for the Memory" (1938). In addition to his work with Robin, Rainger also collaborated with Howard Dietz, Sam Coslow, and Dorothy Parker. He is also a member of the Songwriter's Hall of Fame. Ralph Rainger collaborated with Leo Robin until Rainger's tragic death in a plane crash on October 23, 1942, outside of Palm Springs, CA.