John Herndon Mercer (November 18, 1909 – June 25, 1976) was an American lyricist, songwriter, and singer, as well as a record label executive who co-founded Capitol Records with music industry businessmen Buddy DeSylva and Glenn E. Wallichs.

He is best known as a Tin Pan Alley lyricist, but he also composed music and was a popular singer who recorded his own as well as others' songs from the mid-1930s through the mid-1950s. Mercer's songs were among the most successful hits of the time, including "Moon River", "Days of Wine and Roses", "Autumn Leaves", and "Hooray for Hollywood". He wrote the lyrics to more than 1,500 songs, including compositions for movies and Broadway shows. He received nineteen Oscar nominations, and won four Best Original Song Oscars.