Clarence House has confirmed that the couple will marry next year. They will live in North Wales following a ceremony expected to be in the spring or summer.
According to BBC News, the couple became engaged last month during a private holiday in Kenya.
William, who is is second in the line of succession to the throne behind his father Prince Charles, met Middleton when they were studying at the University of St Andrews in Fife in 2001. Their relationship is believed to have begun in December 2003.
The pair were reported to have split up in 2007, but were later seen at public engagements together.
Prime Minister David Cameron has said that he is "delighted" at news of the Royal engagement and that he wishes the couple "all the best".
On Twitter, Labour leader Ed Miliband added: "Delighted for Prince William and Kate Middleton on their engagement. The whole country will be wishing them every happiness."