She becomes the first female president in AFL/VFL history after winning a ballot contested by other board members Malcolm Speed and Maurice O’Shannassy.
After eight years on the board, O'Neal will take over from Gary March who stood down at the club best and fairest last week.
Born in the United States, O'Neal has lived in Australia for the past 24 years.
During that period Richmond has participated in just three finals series.
This season it participated in its third finals series since 1982 and looks to be a team on the rise.
O'Neal chairs the club’s risk and compliance committee, is a member of the governance committee, and also chairs the Tigers in Community Foundation.
"It is a privilege to lead such a great football club and I look forward to working with the board and management to build on the momentum we have established in recent seasons," O’Neal told richmondfc.com.au.
"This is a strong, united board with great experience, and a number of members could have filled this role. I am honoured that the board felt I was the right person."
O'Neal said she was humbled to be the first woman elected to the role in the history of the competition.
"I think it says much about the Richmond football club’s progressive attitude, broad commitment to diversity and, in this instance, the important role females play in the game at all levels."
O’Neal, was a partner at Herbert Smith Freehills for a number of years and is now a consultant lawyer with Lander & Rogers.
She is recognised as one of Australia’s best lawyers, was a consultant to the Federal Government’s recent Cooper Review of the superannuation system, and currently serves as a non-executive director on the boards of several financial services entities, including MLC nominees, Commonwealth Superannuation Corporation and Retails Responsible Entity Limited.
O’Shannassy will retain the role of vice-president and, along with Speed, fully supported O'Neal's appointment.