Mack was born in Germany but moved with her family to Long Beach, California, when she was 2. She began acting at 4 with print work and commercials, and began studying at The Young Actors Space in Los Angeles when she was 7. She is still currently attending classes there in improvisation and scene study. Before joining the cast of Smallville, Allison starred in the short-lived and sorely under-rated Fox television comedy Opposite Sex. Prior to that, she was a regular on Hiller and Diller, working alongside great talents such as Richard Lewis, Kevin Nealon, and Eugene Levy. Allison has also guest-starred in the WB family drama 7th Heaven as a teenager caught up in the "cutting" trend.

Mack has starred in many movies for television, including the cable film My Horrible Year!, which was directed by Eric Stoltz and starring Karen Allen, Mimi Rogers, and Stoltz himself. She was also in Miss Sherri with Sissy Spacek and Aidan Quinn, Living a Lie with Peter Coyote and Jill Eikenberry, Unlikely Angel with Dolly Parton and Roddy McDowall, and Stolen Memories: Secrets from the Rose Garden starring Mary Tyler Moore and Linda Lavin. Allison is also an accomplished dancer and singer and she currently living in Los Angeles. She enjoys reading, going to movies and plays and spending time with her friends and family.
Announced her engagement to her longtime boyfriend, Peter (March 2003). Attended the 2003 San Diego International Comic-Con with co-star Sam Jones III to promote the 3rd season of Smallville. Allison has a German Shepard/Malamute dog named Phantom. Was listed among the 50 Sexiest Women in the Femme Fatales (January/February 2005) magazine. Had her hair cut short just before the third season of Smallville went into production. After shooting the season opener, the producers insisted that she wear a hairpiece until her hair grew longer. They felt Allison's haircut did not suit the character of Chloe Sullivan. Learned to knit from co-star Annette O'Toole. Shares Kristin Kreuk's addiction to Chapters bookstores. She and her co-star Kristin go shopping often. Audrey Hepburn is her beauty role model. Her younger sister, Robyn, attends the immensely prestigious Orange County High School of the Arts in Santa Ana, California. Born in Germany to American parents, Mindy and Jonathan Mack. The Mack family moved back to the United States from Germany when she was two years old. Her father is an opera singer. An old autographed head shot from when she was a child still lies framed on the wall of a Taco Bell restaurant across the street from Warner Bros. Studios on Olive ave in Burbank, California.