- Is the third youngest of eight children.
- Father worked at the University of Glasgow, and died on the day Peter started school there in 1977.
- While in college, made extra money by entering disco-dancing competitions.
- Was rejected by the National Film School.
- While filming 2000's The Claim in the Canada Rockies, he had to be treated for hypothermia after spending six hours shooting in the snow.
- His 2002 film, The Magdalene Sisters, about Irish-Catholic women accused of sexual misconduct and forced to toil in church-run laundries where they suffer abusive treatment, touched off a dispute with the Vatican.
- In 2009, with three other British actors, he vowed never to work for the BBC again after the broadcaster refused to run a charity appeal for humanitarian aid in Gaza.
- Did a fashion spread in the July 2013 British edition of Esquire magazine.
- 2002, Toronto International Film Festival — Discovery Award: Winner
- 2011, Sundance Film Festival — World Cinema Special Jury Prize: Dramatic for Breakout Performance: Winner
- 0, — :
- 2003, BAFTA Film Awards — The Alexander Korda Award for the Outstanding British Film of the Year: Nominee
- 2013, Emmy — Outstanding Supporting Actor in a Miniseries or a Movie: Nominee
- 2003, BAFTA Film Awards — Best Original Screenplay: Nominee
- 2002, Venice Film Festival — Best Film: Winner
- 1998, Cannes Film Festival — Best Actor: Winner
- 2004, Independent Spirit Awards — Best Foreign Film: Nominee
- 2013, AACTA Awards — Best Guest or Supporting Actor in a Television Drama: Nominee
- Ann Swan — Ex-significant Other
- Patricia Mullan — Mother
- Mairi — Daughter
- Lenny Mullan — Brother
- Charles Mullan — Father
- Katrin — Daughter
- Sophia Mullan — Daughter
- Paddy — Son
- Robina Qureshi — Ex-significant Other
- University of Glasgow, Glasgow, Scotland