O'Loughlin was born on August 24 in Canberra but raised in Sydney, New South Wales, Australia; his year of birth has been given, variously, as 1975, 1976 and 1977. His father is a physics and astronomy teacher in Sydney, Australia. He graduated in 2002 from the National Institute of Dramatic Art. It was rumored that Bon Scott was O'Loughlin's biological father, however this is false. He resides in West Hollywood, California. He is currently starring in the CBS television series, Hawaii Five-0.
O'Loughlin's film career started off in 2004 when he landed his first lead role in the film Oyster Farmer. Continuing his career O'Loughlin appeared in Man-Thing, Feed, and the Australian mini-series The Incredible Journey of Mary Bryant for which he received nomination for the AFI Award in 2005 and a Logie Award in 2006. O'Loughlin joined the cast of The Shield in 2007 as Detective Kevin Hiatt, the newest member of the strike team. He left The Shield after he won the lead role on the CBS series Moonlight, where he played private investigator and vampire Mick St. John. The filming of Moonlight was interrupted by the Hollywood writers strike. There was speculation that the series would be dropped but fan pressure prevailed and the show was given four additional episodes to try to regain its audience share. Despite being the highest rated show in its Friday evening slot (consistently achieving over 7 million viewers), CBS did not commission a second season. After its cancellation a fan-based charity campaign to try to bring back Moonlight by holding blood drives proved unsuccessful.
In August 2008, it was announced that CBS had cast O'Loughlin as the star of a new show, called Three Rivers, developed by producer Carol Barbee. James Bond role In 2005, he received a boost in celebrity as a candidate for the role of James Bond. On 7 August 2005, he confirmed to The Daily Telegraph that he had tested for the role, but ultimately, the part went to Daniel Craig. Director Martin Campbell stated that only Sam Worthington and Henry Cavill were in serious contention along with eventual winner Craig.
In 2005 O'Loughlin was nominated Best Lead Actor in Television for his work in The Incredible Journey of Mary Bryant at the Australian Film Institute Awards. At the Logie Awards of 2006 he was nominated Most Outstanding Actor in a Drama Series for the same film.
In February 2010, it was announced that O'Loughlin was cast in the CBS reboot Hawaii Five-0 portraying Steve McGarrett, which premiered on September 20, 2010.
He has a faded tattoo on each forearm, tattoos on each shoulder, one tattoo over his right nipple, a compass and cross on his upper back, a swallow on his neck and finally, an enormous "tramp stamp" on his lower back *g*