The first cast member hired was Gilda Radner. The rest of the cast included fellow Second City alumni Dan Aykroyd and John Belushi, as well as National Lampoon "Lemmings" alumnus Chevy Chase (whose trademark became his usual falls and opening spiel that cued the show's opening) who was chosen as anchor for Weekend Update, Jane Curtin, Garrett Morris, and Groundlings alumna Laraine Newman. The original head writer was Michael O'Donoghue, a writer at National Lampoon who had worked alongside several cast members while directing The National Lampoon Radio Hour. The original theme music was written by future Academy Award–winning composer Howard Shore, who – along with his band (occasionally billed as the "All Nurse Band" or "Band of Angels") – was the original band leader on the show. Paul Shaffer, who would go on to lead David Letterman's band on Late Night and then The Late Show, was also band leader in the early years.

Much of the talent pool involved in the inaugural season was recruited from the National Lampoon Radio Hour, a nationally syndicated comedy series that often satirized current events.

This would be the only season for George Coe and Michael O'Donoghue as official cast members. While Coe was billed only in the premiere, he was seen in various small roles through the season before leaving the show altogether. O'Donoghue was credited for the first, third, and fourth episodes and would continue to work for the show as a writer, as well as an occasional guest performer (particularly as "Mr. Mike"), through season 5.
The Not Ready for Prime Time Players
• Dan Aykroyd
• John Belushi
• Chevy Chase
• George Coe (only episode: October 11, 1975)
• Jane Curtin
• Garrett Morris
• Laraine Newman
• Michael O'Donoghue (final episode: November 8, 1975)
• Gilda Radner
Bold denotes Weekend Update anchor

The original writing staff included Anne Beatts, Chevy Chase, Tom Davis, Al Franken, Lorne Michaels, Marilyn Suzanne Miller, Michael O'Donoghue, Herb Sargent, Tom Schiller, Rosie Shuster and Alan Zweibel. Michaels did not designate a head writer in the early years, despite Chase and O'Donoghue claiming that they were head writers, according to various SNL books.