One of the two images by Mario Testino shows the couple, dressed in jeans and casual tops, smiling in each others' arms. The other, more formal, depicts them standing together in a state room at St. James's Palace.
The pictures, released Sunday by the prince's office, were taken by fashion photographer Testino, a royal family favorite who captured some of the most iconic images of William's late mother, Princess Diana.
Testino said the couple appeared "in their prime and brimming with happiness" when he photographed them on Nov. 25.
"I have never felt so much joy as when I see them together," he said.
The Peruvian photographer, who made his name shooting models like Kate Moss, took a series of glamorous black-and-white images of Diana that were published in Vanity Fair in 1997, shortly before her death in a Paris car crash.
William, who is second in line to the British throne, has inherited his mother's poise. In both pictures he and Middleton appear entirely comfortable with the camera and each other.
In the formal photos the couple stands on a red carpet in the palace's Council Chamber -- in front of oil paintings of some of William's ancestors -- smiling toward the camera, as Middleton rests her left hand on her fiance's forearm. He wears a gray suit and blue tie over a white shirt, she a smart white dress from Reiss.
The more intimate picture shows the pair smiling broadly as they embrace in front of a window at the palace, with William wrapping his arms around Middleton while she puts her left hand on his chest. Clearly visible is the engagement ring William gave her -- an oval sapphire surrounded by diamonds that belonged to his mother.
Both wear jeans, with Middleton sporting a blouse from mid-market retailer Whistles and William wearing a brown sweater over a white shirt from traditional tailors Turnbull and Asser.
William and Middleton, both 28, announced last month that they will marry on April 29 at Westminster Abbey in London.
Testino has often photographed members of the royal family, taking portraits to mark Prince William's 21st birthday in 2003 and his younger brother Prince Harry's 20th birthday the next year. He also has photographed their father, Prince Charles, for Vogue magazine.