He started acting with Theatre Corporate, Auckland in the late 1970s. Early roles in New Zealand were in Sea Urchins a 1980-84 New Zealand TV series, the 1982 films The Scarecrow and Beyond Reasonable Doubt, the 1985 film Came a Hot Friday, and as Captain Gordon Vette in the 1988 miniseries Erebus: The Aftermath.

In 1999, Billing was nominated in the ‘Best Actor in a Supporting Role’ award at the AFI Awards for his role in Siam Sunset. In 2009, Billing won the ‘Best Actor in a Television Drama’ award at the AFI Awards, and was nominated for the ‘Outstanding Actor’ award at the 2010 Logies for his role in Underbelly.

Billing has starred in many television shows and had main roles on Bad Cop, Bad Cop, Dossa and Joe and Hell Has Harbour Views. Billing also had a recurring role on Blue Heelers as Senior Constable Ian Goss, on Always Greener as Eddie McGill, in Packed to the Rafters as Ron Barrett, and in Under the Mountain. In 2000 he featured in the film The Dish, portraying the Mayor of Parkes in a comedy about the moon landings. He also appeared as part of the ensemble on the 2006 season of Thank God You’re Here. He has had a guest role on All Saints.

In 2009, Billing played Griffith drug lord Robert Trimbole in the high-rating drama series Underbelly: A Tale of Two Cities, starring alongside Matthew Newton. He also starred in the film Charlie and Boots. Billing played the part of Chief Dufflepud in the 2010 film The Chronicles of Narnia: The Voyage of the Dawn Treader as well as a recurring character in the Nine Network police drama Cops L.A.C..

Billing’s career achievements were honoured in 2009 when he was inducted into the Australian Film Walk of Fame.

From 2012 Billing has played Harry Strang in the Jack Irish television drama series and television movies adapted from the detective novels by Peter Temple.

In 2013, he appeared in the New Zealand television comedy Agent Anna, for which he agreed to be paid at New Zealand rates.

On 26 January 2015, Billing was awarded the Medal of the Order of Australia for “service to the performing arts, particularly as an actor, and to the community”.

In 2020, Billing starred in the Australian comedy-drama film Never Too Late.