Mr King was admitted to the bar in Dunedin in 1993. Since then he has been counsel in more than 350 jury trials. Of those, about 50 have been homicide cases.
He has defended some of New Zealand's most high-profile killers, and been successful in getting acquittals for others facing murder charges.
In 2009 Mr King was on the defence team for Clayton Weatherston, who murdered his ex-girlfriend Sophie Elliott. On his website he described Weatherston's as "undoubtedly one of the most unpopular trials of modern times".
In 2008 he represented Daniel Moore, who was convicted at trial of the murder of Tony Stanlake, whose handless corpse was found on a Wellington beach.
Mr King also hit the headlines for his work on the case of John Barlow, who was tried three times and convicted for the murders of Wellington businessmen Gene Thomas and his son Eugene Thomas. He was unsuccessful in an appeal against that conviction to the Privy Council but continues to work on the case.
Mr King is no stranger to the television screen. He was the host of TVNZ7's The Court Report, taking the public behind the scenes and explaining legal issues and cases in-depth.
Away from the ceremony of the court room, Mr King's main focus is his family, who live with him in Lower Hutt.
"Greg has been actively landscaping the property over the last 10 years. The family share their home with four 'rescued' cats, four chickens and a Scottish Terrier named Holly," his website says.
"Greg is also an avid sports fan. He has previously coached boxing, including training All Black legend Bernie Fraser for the 2002 Fight for Life. Greg is a former president of the Otago Boxing Association. Other favoured sports include rugby union, rugby league, cricket and netball."