Guðmundur Hafsteinsson was born in Reykjavík, Iceland, in 1953. His musical education began in 1969 with private piano study under the tutelage of Málfríður Konráðsdóttir. Two years later he entered the Reykjavík College of Music, where he continued his piano studies with Halldór Haraldsson.

In autumn 1977 Hafsteinsson went to New York City to study composition and became a student of Charles Wuorinen. He entered The Juilliard School in 1979 as a student of Vincent Persichetti and received the Doctor of Musical Arts degree in composition from Juilliard in 1986, having been awarded the Irving Berlin Fellowship while a graduate student. He studied conducting with David Gilbert in 1985-1986. During and afterhis graduate studies, Hafsteinsson served as an adjunct faculty member at Juilliard for two years.

Hafsteinsson returned to Iceland in 1987 and joined the faculty of the Reykjavík College of Music, where he taught music theory and composition for thirty years.

Hafsteinsson’s music has been performed in the US and Europe, as well as in Iceland, and he has participated in its performance as conductor, pianist, and cimbalomist.