Marini attended North Texas State University College of Music (now known as the University of North Texas College of Music), where he played in the One O'Clock Lab Band. From 1972 to 1974 he played in Blood, Sweat & Tears. From 1975 to 1983, he was a member of the "Saturday Night Live" house band. He was a member of The Blues Brothers band, appearing in "The Blues Brothers" movie and its sequel, "Blues Brothers 2000", playing the part of "Blue Lou", a moniker given by Dan Aykroyd.