Born in Vienna, Grell received violin lessons at the age of eight; at 14 he founded a dance band with school mates, one year later he started playing the clarinet.
After graduating from high school and completing his military service from 1943 to 1945, he studied musicology at the University of Vienna and violin and clarinet, later composition at the Music and Arts University of the City of Vienna with Hugo Zelzer and conducting with Kurt Wöss.
[3] In addition to his engagements as a violinist in various dance orchestras, from 1949 he worked as an arranger for the radio station Rot-Weiß-Rot.
Grell died in Vienna on 6 September 2003 at the age of 78 and was buried at the Hütteldorf cemetery [de] (Group 2, Number G8).
[4] In the Helmut-Qualtinger-Hof [de], in which Karl Grell lived, stands a memorial stone for him erected in 1958/59 according to the plans of Josef Schuster.