Emma Lou Diemer was born in Kansas City, Missouri. She began to play and compose piano music as a young child, and became the organist in her church at age 13. As an adult, she majored in composition at Yale University and the Eastman School of Music. She spent a year studying composition and piano in Brussels on a Fulbright Scholarship and also studied composition at Tanglewood. After receiving her doctorate from Eastman, she wrote music for the Arlington, Virginia schools under a Ford Foundation Young Composer's grant and joined the faculty of the University of Maryland.

In 1971, Diemer moved to Santa Barbara, CA, where she was a professor at the University of California. She was composer-in-residence with the Santa Barbara Symphony from 1990-92.

The symphony has performed five of her works including a marimba concerto, a piano concerto (which won a Kennedy Center Friedheim award), two overtures, and a recent short work on Chumash Indian themes for the 2004 Young People's Concerts. Diemer has written for many mediums: solo instruments, solo voice, chamber, instrumental and choral ensembles, orchestra, band, and electronics. Her music, much of it commissioned, has been published since 1957. Some of her piano music has been recorded, including the piano concerto and chamber music that includes piano.

Diemer likes to write music of varying levels of difficulty and no matter whether the music is easy or difficult, she intends for it to be communicative and thought-provoking, as well as useful.