Shaffer began his music career in 1972 when Stephen Schwartz invited him to be the musical director for the Toronto production of "Godspell", starring Victor Garber, Gilda Radner, Martin Short, Eugene Levy, Dave Thomas, and Andrea Martin. He went on to play piano for the Schwartz Broadway show "The Magic Show" in 1974, then became a member of the house band on NBC's "Saturday Night Live" ("SNL") television program from 1975 to 1980 (except for a brief departure in 1977). Though Shaffer was at the piano and appeared to be directing the band's actions, Howard Shore was credited as "SNL"'s musical director, eventually turning the actual conducting of the band to Howard Johnson. Shaffer also regularly appeared in the show's sketches, notably as the pianist for Bill Murray's Nick the Lounge Singer character, and as Don Kirshner. He also appeared as a keyboardist on the 1978 album, "Desire Wire", recorded by pop/rock star, musician, and backing vocalist Cindy Bullens.