King County prosecutor's office spokesman Dan Donohoe said the jury's verdict had taken account of the presence of Ms Hockley's 13-year-old daughter, Maggie, as an aggravating factor.
Maggie had raced outside to find her mother unconscious on the home's driveway.
Mr Donohoe said the verdict also took account of Wiggins' domestic violence against other women as a second aggravating factor.
The exceptional sentence of 30 years in prison took account of both aggravating factors. The standard sentence is up to 23 years in prison.
Ms Hockley, originally from Nelson and educated at Canterbury University, moved to Seattle in 1978.
Police said she left her home about 11pm on Christmas Eve to speak with a friend.
Witnesses reported hearing a thump and seeing a man walk away and drive off in a car.
Ms Hockley died in hospital on Christmas Day from blunt-force trauma to the head.
