Born in Florida, USA, Hammill graduated from the Juilliard School in New York. He studied horn with C. Wahl (Florida Orchestra), J. Lanzmann (Metropolitan Opera Orchestra), and D. Clevenger (Chicago Symphony Orchestra). Hammill performed as a member of the Civic Orchestra of Chicago in 1999. He won the second prize in the 72nd Music Competition of Japan. He has performed with leading orchestras in the USA, UK, and Japan, including the Chicago Symphony, London Symphony, NHK Symphony, Tokyo Philharmonic, New Japan Philharmonic, Japan Philharmonic, Sapporo Symphony, Nagoya Philharmonic, and Kansai Philharmonic orchestras. As a horn instructor, he regularly teaches at Dolce Musical Instruments' Music School, the British School, and Elizabeth University of Music. Hammill is also an active member of Tsunobue Horn Ensemble. He currently serves as Principal Horn of the Tokyo Symphony Orchestra.