Philomena Lee, an Irishwoman in her 70s, became pregnant as a teenager in 1952. Her family abandoned her out of shame and sent her to a convent, where, along with other young girls in the same predicament, she was regarded as "a fallen woman."
Three years later, the nuns made her give up her son Anthony, to be sold for adoption in America. Lee, who was forced to sign a document promising "never to seek to know" what happened to her son, later moved to England where she married and had a family.
Through a lucky set of circumstances she happens to meet Martin Sixsmith, an ex-BBC reporter. When Philomena tells Martin about her long search for her son, he realizes that hers is a remarkable story. He arranges for the two of them to visit the United States to find out what happened to Anthony.