Graduated from Harvard University and University of California, Los Angeles, She started her career in the 1980s as an assistant to Suzan Bymel, with whom she founded the agency Bymel O'Neill & Associates in 1994. In 1999, the company merged with the More Medavoy to the Talent Entertainment Group'.
In 2002, O'Neill and Bymel, together with Eric Kranzler, David Seltzer, Guymon Casady and Daniel Rappaport founded the Management 360 talent and literary management company. In 2009, The Hollywood Reporter named her the 90 in their #100 Most Influential Women in the Entertainment Industry.
