Allison Christin Mack was born on July 29, 1982, in Preetz, West Germany, to American parents Jonathan Mack, an opera singer, and Mindy Mack, a schoolteacher and bookkeeper. The family moved to Long Beach, California, when she was two years old.

Growing up in a creative household, Allison was introduced to the arts at an early age. She has an older brother, Shannon, and a younger sister, Robin. Her parents' support and the artistic environment of her upbringing played a significant role in nurturing her interest in acting.

Allison Mack began her acting career at the age of four, starting with print work and commercials. By the age of seven, she was studying at The Young Actors Space in Los Angeles, honing her craft.

Her early television appearances included roles in "7th Heaven" and "Opposite Sex." In 2001, she secured the role of Chloe Sullivan in "Smallville," a role that would define her career and earn her critical acclaim. She also directed two episodes of the series, showcasing her versatility.

Following "Smallville," she appeared in "Wilfred" and other projects, though none matched the prominence of her earlier work. Her film credits include roles in "My Horrible Year!" (Eric Stoltz's directorial debut), "Camp Nowhere," and the Disney film "Honey, We Shrunk Ourselves." She also voiced Clea, a museum curator, in an episode of "The Batman."

Her personal life has been marked by her involvement in NXIVM, a cult and multi-level marketing company. In 2018, she was arrested by federal authorities on charges of sex trafficking, sex trafficking conspiracy, and forced labor conspiracy related to her involvement in NXIVM and its subgroup, DOS.

She pleaded guilty to racketeering and racketeering conspiracy charges and in 2021 was sentenced to three years in prison. She served 21 months in Federal Correctional Institution, Dublin, in California and was released in July 2023.

She married actress Nicki Clyne in February 2017, but their marriage ended in divorce in December 2020. Her net worth is estimated at $2 million.