The ratings, which range from TV-Y for "all children" to TV-MA for "mature audiences only," typically appear in a black box in the first few seconds of an episode.
Some sites, such as Hulu, already display the content ratings.
According to a recent survey by the TV Parental Guidelines Monitoring Board, which oversees the rating system, about 70 percent of parents use TV ratings to help choose programming. The study also found that 61 percent of children now watch shows on devices other than a television screen.
Federal Communications Commission (FCC) Chairman Julius Genachowski applauded the announcement.
“With our rapidly changing media marketplace, it is vital parents have tools to help them make informed choices,” he said in a statement.