After college, she returned to Minneapolis, in 1993 where she joined her sister Andrea Wallack in establishing a national presence for NightOwl Discovery, a company specializing in data discovery, governance and compliance for heavily regulated industries. When the company expanded to the West Coast in 1995, Wallack moved to Los Angeles and, after "meeting a lot of writers", decided to become a screenwriter herself.[1][5] She partnered with Craig Borten to write the screenplay for Dallas Buyers Club, which was based on the true story of AIDS activist Ron Woodruff.[1] Although Wallack and Borten sold the script in the 1990s, the film did not enter production for several years and was released in 2013, almost 20 years after it had been written.[5]Dallas Buyers Clubreceived numerous accolades, including an Academy Award nomination for Best Original Screenplay for Wallack and Borten.[5]
After selling the script for Dallas Buyers Club, Wallack was named one of Variety magazine's "10 screenwriters to watch" in 2005.[1] Her first feature film to be produced was Meet Bill, which Wallack wrote and directed with her husband, Bernie Goldmann, and which was released in 2007.[5] She created the story for the 2012 film Mirror Mirror, an adaptation of the Snow White fairy tale starring Julia Roberts.[4]
Wallack's future projects include the screenplay of Emily the Strange[4] and a rewrite of The Last Witch Hunter.[6]
In 2021, an article by AIDS activist Peter Staley described Wallack as an AIDS denialist and detailed the experience of attempting to remove more than 30 inaccurate claims about AIDS from her original script for Dallas Buyers Club.[7]