The award reflects who editors and broadcasters think was the most influential person in entertainment and culture in 2011.
Lady Gaga beat the late Apple founder Steve Jobs by just three votes. Many others received numerous votes, including Taylor Swift, Charlie Sheen, Adele and the cast of "Harry Potter."
The mega pop star won three Grammys earlier this year, including one for her album "The Fame Monster," while also advocating for tolerance and equality.
When the album was released in May, 1.1 million copies sold in the first week, partly aided by a dramatic discount from Amazon, which sold it for 99 cents. But it was an industry-shattering moment because an extraordinary 60 percent of sales in the first week were digital downloads. Altogether, it outsold the next 42 albums on the Billboard chart combined.
According to Forbes magazine, which compiled pretax income earned from May 2010 to May 2011, Lady Gaga earned $90 million.
Previous winners of the AP Entertainer of the Year include Betty White, Swift, Tina Fey and Stephen Colbert.
The Associated Press contributed to this report.