The Team Will finalist from the Blue Mountains pipped runner-up Jackson Thomas from Team Ricky.
ZK (Team Will) and Frank Lakoudis (Team Joel) were the first to be eliminated, followed by Johnny Rollins (Team Kylie).
For Nissen it was second time lucky, who previously made it to the semi finals of Australia’s Got Talent at the age of 12.
“Thank you Australia! Thank you, thank you, thank you…. oh my God this is surreal!” she said.
Her coach will.i.am capped off her night by announcing, “I would like to sign Anja to my label!” (but she already has a contract with Universal, plus $100,000 prize money and a new car.
The winner’s single My Girls, will be released on Friday, July 25 and the winner’s album will be released on Friday, August 1.
The grand final saw coaches performing duets (and one quintet) with their finalists including on Can’t Get You Out of my Head, Where is the Love?, Every Breath You Take and Radioactive.
All 16 finalists also joined in the opening number, a group performance of Aussie classic The Real Thing. Also performing were Sheppard and a baffling but dazzling duet staged by will.i.am and Cody Wise (hats off to the show’s director for that one).
Ricky Martin also offered Jackson Thomas a spot on his Australian tour.
Nine’s series has underpinned Nine’s post Easter ratings, and spawned The Voice: Kids.
Nine has already announced auditions for 2015.
This post updates.