[1] She is the founder and co-CEO of the Dart Group, now known as 42West,[2] which prior to its 2017 acquisition was the largest independently-owned public relations firm in the entertainment industry.

She has represented actors including Meryl Streep, Nicole Kidman, Daniel Day-Lewis, Tom Hanks, and Jessica Lange, and directors Martin Scorsese, Francis Ford Coppola, Jonathan Demme, Mike Nichols, and Sydney Pollack.

In 2001 a photo of Dart, Kingsley and Smith ran in the "Legends of Hollywood" issue of Vanity Fair with the caption "Not since the heyday of MGM have three little letters wielded so much power.

For many years, Ms. Kingsley, based in Los Angeles, and Ms. Dart, her New York-based partner in privately held PMK, were indisputably the most influential among them.

[21] The filmmakers and actors who left PMK for the Dart Group included Demme, Hanks, Jessica Lange and Mike Nichols.

[23][24][4] Dart joined the Board of Directors of 42 West's parent company, Dolphin Entertainment in June 2020 and currently serves as its Strategic Advisor.

"[1][13] This controversially[8] included film director Woody Allen, who Dart had represented since the mid-1980s and who faced allegations of sexual assault against his adoptive daughter.

Variety wrote: "Even the efforts of Allen’s longtime publicist, Leslee Dart, to counter the initial tide of negative stories itself became a news item.

[34] In 2015, 20 years after she orchestrated Hugh Grant's mea culpa on the Tonight Show following his arrest for lewd conduct; The Independent wrote that it was "the greatest PR save of all time.