[3][4] Prior to NBCUniversal, Lack held a series of media executive positions, including as the chairman and CEO of Bloomberg Media Group; chairman and CEO of Sony Music Entertainment; and president and chief operating officer of NBC.

[1] In 1976, Lack was hired by 60 Minutes creator Don Hewitt at CBS News as a producer for the personality-driven television show Who's Who.

[15][16] His work as a CBS producer includes "The Boat People" (about Vietnamese refugees),[17] "Teddy" (about Ted Kennedy)[18] and "The Defense of the United States" (about the Cold War) with Walter Cronkite.

[3] In 2001, Lack left the news division to become president[20] and chief operating officer of NBC, the television network.

Lack became CEO of the new Sony BMG, a 50–50 venture with Germany's Bertelsmann that resulted in the second-largest music company in the world.

[20] At Sony BMG, he pushed the company further into video, including television programming, and had to contend with the erosion of sales because of music file-sharing services such as Napster.

[24] He later created SonyBMG Films,[25] a division that produced numerous titles including Cadillac Records starring Beyonce.

[40][41] In January 2017, Lack announced the hiring of Megyn Kelly away from Fox News saying in a memo, "She's demonstrated tremendous skill and poise, and we're lucky to have her.

[43] In late October 2018, Business Insider reported that Kelly would depart the network following controversial remarks on the nature of blackface.

[44] In 2019, investigative journalist Ronan Farrow claimed that Lack downplayed a human resources complaint of rape against Today anchor Matt Lauer.

Farrow also alleged that Lack had ordered Richard Greenberg to block reporting on the Harvey Weinstein sexual abuse cases.

[46][47] On October 10, 2017, The New Yorker ran a story by Farrow about Weinstein with seven named women accusing him of sexual misconduct.