McKidd was born and brought up in Elgin, the north-east of Scotland, the son of Kathleen, a secretary, and Neil McKidd, a plumber. He attended Seafield Primary School and Elgin Academy, and was a member of the local amateur dramatic group, Moray Youth Theatre. Planning to study engineering, he attended the University of Edinburgh, but dropped out and instead enrolled at Queen Margaret College in Edinburgh to study drama. He also joined Edinburgh University's student theatre company, Bedlam Theatre where he performed as a member of the improvised comedy troupe The Improverts.
After playing Tommy in Trainspotting, McKidd was cast as Father Deegan in the 1996 Christmas episode of Father Ted. Subsequent roles include Malky Johnson in Small Faces. In 2004, he played James Hepburn, 4th Earl of Bothwell, the third husband of Mary, Queen of Scots, in the BBC mini-series Gunpowder, Treason & Plot.
In 1999 he was part of an ensemble cast in Mike Leigh's Topsy Turvy, based on the writing and rehearsal for Gilbert and Sullivan's The Mikado. The actors researched their historical characters and used this knowledge during extensive rehearsals to help develop dialog for scenes blocked out by Leigh. McKidd, like the rest of the cast, did his own singing in the Gilbert & Sullivan operettas portrayed in the film.
In 2001 he played Elliot in a British film by Caleb Lindsay called Understanding Jane. He appeared in Ridley Scott's Kingdom of Heaven, the 2002 film adaptation of Nicholas Nickleby. In Neil Marshall's horror film, Dog Soldiers, he appeared as Pte Lawrence Cooper. In the 2005 BBC drama, The Virgin Queen, he played Thomas Howard, 4th Duke of Norfolk.
In 1998, McKidd was in the four-part BBC2 series Looking After Jo Jo, playing the role of Basil. He was also one of the main stars of the joint HBO/BBC series Rome, where his portrayal of the soldier/politician Lucius Vorenus received critical acclaim. The role gained him recognition in the US.
Additional work includes his role in the Silence of the Lambs prequel Hannibal Rising (2007). In late 2007, McKidd began his role as the lead character in the American Fantasy television series Journeyman on NBC. The show suffered from low ratings and only thirteen episodes were produced.
His role in Rome led to McKidd's casting in the medical drama series Grey's Anatomy as Dr. Owen Hunt. He made his directorial debut in the series' seventh season, directing the episode "Don't Deceive Me (Please Don't Go)". McKidd commented of the debut, "It's something I've really wanted to do for a long time. Shonda Rhimes and the producers all supported me and gave me the chance, and when you think it costs around $5 million to make an episode, that's a lot to hang on an actor who really hasn't had any experience." He won the award for "Best Performance in a Drama Series Multi-Episode Storyline" at the 14th Prism Awards for his work in "Grey's Anatomy".
McKidd has done voice work and voiced the character of Jezz Torrent, flame haired lead singer of the fictional Scottish hard rock back Love Fist in the video games "Grand Theft Auto: Vice City". He is also credited with playing a voice-over for the character John "Soap" MacTavish in Call of Duty: Modern Warfare 2 and Call of Duty: Modern Warfare 3. McKidd was in talks in 2008 to portray Conner Macleod in a big screen remake of the 1986 fantasy movie Highlander though the role eventually went to Ryan Reynolds.
McKidd instigated a Scottish folk music album that was recorded in 2011/2012 at Hogmanay in his home town of Elgin. Many of the contributors to this "collective" album are old school friends of McKidd's. The album was released on 15 June 2012 in aid of Save the Children.
Many of the tracks on the album are Scottish folk songs that were handed down through the generations including Now Westlin Winds, Both Sides the Tweed, Charlie is My Darlin', The Water is Wide, The Fairie Dance, Fareweel Tae Tarwathie, laun Ghlinn Cuach, Muckin' O' Geordie's Byre, The Lea Rig, Barnyard's O Delgaty, John Anderson, Raggle Taggle Gypsy, Diane of Pitgaveny and These are My Mountains.
Contributors to the album include Nick Lloyd Webber, Jamie D Reid, Bryan Tolland, Paul Anderson, Shona Donaldson, Dave Martin, Delane Morrison-Wallace, Morna Young, Carron Anderson, Ali Napier, Dan Conroy, Rose Millett, Garry Morrison, Bob Sharp, Jen Lunan, Carey Lunan and Donald Lunan.
According to accounts from McKidd's tweeting, this seems to be one of his most personal projects to date.
McKidd married Jane Parker in 1999, and they have two children, Joseph and Iona. The family resides in Los Angeles during filming of Grey's Anatomy, but try to go back to Scotland or the UK at least twice a year.
Playing a doctor has led the actor to support the P3 Project, a friend's charity focusing on African paediatric care.
- Small Faces (1996) Malky Johnson
- Trainspotting (1996) Tommy
- Behind the Lines (1997) Callan
- Richard (1997) Henry Percy
- Hideous Kinky (1998) Henning
- Bedrooms and Hallways (1998) Leo
- The Acid House (1998) Johnny (A Soft Touch)
- Dad Savage (1998) H
- Looking After Jo Jo (1998) Basil
- Topsy-Turvy (1999) Durward Lely (Nanki-Poo)
- Anna Karenina (2000) Count Vronsky
- Understanding Jane (2001) Eliott
- Nicholas Nickleby (2002) John Browdie
- Max (2002) George Grosz
- Dog Soldiers (2002) Pvt. Lawrence Cooper
- That Old One (2002) Tom Furness
- The Key (2003) Duncan
- AfterLife (2003) Kenny Brogan
- 16 Years of Alcohol (2003) Frankie
- Does God Play Football (2003) Father Davis
- De-Lovely (2004) Bobby Reed
- The Purifiers (2004) Moses
- One Last Chance (2004) Seany
- Kingdom of Heaven (2005) English Sergeant
- The Rocket Post (2006) Thomas McKinnon
- The Last Region (2007) Wulfila
- Hannibal Rising (2007) Kolnas
- Made of Honor (2008) Colin McMurrary
- One Night in Emergency (2010) Peter Forbes
- Percy Jackson & the Olympians: The Lightning Thief (2010) Poseidon
- Bunraku (2010) Killer #2
- The Great Ghost Rescue (2011) Hamish
- Comes A Bright Day (2012) Cameron
- Brave (2012) Lord MacGuffin/Young MacGuffin
- Father Ted (1996) Father Deegan
- The Magical Legend of the Leprechauns (1999) Jericho O'Grady
- Anna Karenina (2000) Count Vronsky
- North Square (2000) Billy Guthrie
- Gunpowder, Treason & Plot (2004) Bothwell
- The Virgin Queen (2005) Duke of Norfolk
- Rome (2005-2007) Lucius Vorenus
- Journeyman (2007) Dan Vasser
- Grey's Anatomy (2008-present) Dr. Owen Hunt
- Grey's Anatomy (2011) "Don't Deceive Me (Please Don't Go)"
- Grey's Anatomy (2011) "Poker Face"
- Grey's Anatomy (2012) "Let the Bad Times Roll"
- Grey's Anatomy Grey's Anatomy: Message of Hope (webisodes)
- Grand Theft Auto: Vice City (2002) Jezz Torrent
- Call of Duty: Modern Warfare 2 (2009) Captain John "Soap" MacTavish
- Call of Duty: Modern Warfare 3 (2011) Captain John "Soap" MacTavish