Main Cast:
* Hugh Grant as David, the Prime Minister
* Liam Neeson as Daniel, a widower trying to bond with his stepson
* Colin Firth as Jamie, a British author who falls in love with a Portuguese woman
* Laura Linney as Sarah, Daniel's sister who is in love with her colleague
* Emma Thompson as Karen, Daniel's sister who is going through a difficult marriage
* Alan Rickman as Harry, Karen's husband who is having an affair
* Keira Knightley as Juliet, a young woman who falls in love with her best friend's brother
* Chiwetel Ejiofor as Peter, Juliet's best friend
* Bill Nighy as Billy Mack, a struggling rock star
* Martine McCutcheon as Natalie, a young woman who falls in love with the Prime Minister
* Thomas Sangster as Sam, Daniel's stepson
* Rowan Atkinson as Rufus, an employee who is helping Sam learn the drums
* Andrew Lincoln as Mark, a man who is secretly in love with his best friend's wife
Supporting Cast:
* Lucia Moniz as Aurelia, Jamie's love interest
* Heike Makatsch as Petra, Harry's mistress
* Kris Marshall as Colin, a British man who travels to America for work and falls in love
* Shannon Elizabeth as a woman who is attracted to Colin
* Abdul Salis as the Prime Minister's aide
* Nina Sosanya as Annie, a single mother
* Gregor Fisher as the Christmas party guest
* James McAvoy as the man who helps Annie
* Billy Boyd as the wedding singer
* Judy Dench as the voice of the narrator
This is not an exhaustive list, but it includes most of the major roles in the film.