Forbes magazine ranked Winfrey, 59, ahead of Hollywood titans Steven Spielberg and Clint Eastwood and towering over other TV figures such as journalist Barbara Walters and financial guru Suze Orman.
Forbes said that 48 percent of people surveyed rated Winfrey as influential, down just one point from last year. The list was drawn from polls of Americans conducted by E-Poll Market Research, which ranks more than 7,500 celebrities based on 46 different personality attributes.
Winfrey ended her daily "The Oprah Winfrey Show" in May 2011 after 25 years to launch the Oprah Winfrey Network (OWN), which features lifestyle programming aimed at women.
After struggling in the ratings since its launch, OWN has seen audiences rise recently, thanks to Winfrey's January world exclusive with cyclist Lance Armstrong admitting to years of doping, and her wide-ranging interview with R&B singer Beyonce.
Forbes noted that Winfrey's magic had rubbed off as well, with one of her protges, TV physician Dr. Mehmet Oz, ranking sixth on the list.
Film directing, however, seems to be the profession most associated with influence, as four directors, including Ron Howard and Martin Scorsese, crowded into the Top 10.
E-Poll Chief Executive Gerry Philpott said that while influence could mean different things to different people, most often it reflects someone's impact on the culture.
Reflecting on Spielberg's runner-up ranking, Philpott said "To this day, ask anyone what they think about before going in the ocean," referring to the filmmaker's 1975 blockbuster "Jaws."
Dropping out of the Top 10 entirely was last year's No. 2 finisher, actor Michael J. Fox, who has been out of the public eye of late.
Eastwood, who made headlines by addressing an empty chair at the 2012 Republican National Convention, rounded out the Top 10.
The Top 10 Most Influential Celebrities of 2013, according to Forbes are;
1. Oprah Winfrey
2. Steven Spielberg
3. Martin Scorsese
4. Ron Howard
5. George Lucas
6. Dr. Mehmet Oz
7. Barbara Walters
8. U2 frontman Bono
9. Suze Orman
10. Clint Eastwood
The full list can be seen at http://www.forbes.com/sites/dorothypomerantz/2013/03/14/oprah-winfrey-tops-our-list-of-the-most-influential-celebrities/
(Reporting by Chris Michaud, editing by Jill Serjeant)