Niemack sang in a church choir from age seven. She decided on a professional career in singing at age 17, and soon after met Warne Marsh, who encouraged her to explore jazz. She studied jazz at Pasadena City College, and later at the New England Conservatory of Music and the Cleveland Institute of Music.
Her debut album was released in 1977; she has recorded several albums under her own name in addition to working with Toots Thielemans, James Moody, Lee Konitz, Clark Terry, Kenny Barron, Fred Hersch, Kenny Werner, Joe Lovano, Eddie Gomez, and the Widespread Depression Jazz Orchestra. She has toured Europe many times and also teaches music.
- By Heart (Sea Breeze Records, 1977)
- Blue-Bop (Freelance Records, 1988)
- Long as You're Living (Freelance, 1990)
- Straight Up (Freelance, 1992)
- Heart's Desire (Stash Records, 1992)
- Mingus, Monk & Mal (Freelance, 1995)
- Night and the Music (Freelance, 1996)
- About Time (Sony Records, 2003)
- Jazz Singers' Practice Session (Gam Records, 2003)
- What's Going On? (Temps Records, 2007)
- Blue Nights (Blujazz, 2007)
- In The Sundance (Blujazz, 2009)