The 2008 Olympic Games champion dominated the final in Berlin, posting a best throw of 20.44m to retain the world crown she first won two years ago in Japan.
She finished comfortably ahead of silver medallist, German Nadine Kleinert, who threw a career best 20.20m, and China's bronze medallist Lijao Gong, who managed a personal best of 19.89m.
Vili, 24, worked her way into the final and was as low as fifth after the second round before hitting the lead with her third effort of 20.25m.
She opened with 19.40m, then stepped out of the circle to record a no throw with her second effort.
Vili grabbed the lead with her third throw, a lead she would not relinquish, then extended it with her fifth of 20.44m.
Earlier, Vili had struck an early psychological blow by easily qualifying for the final by throwing 19.70m with her first attempt, well clear of the 18.50m required to automatically advance, to advance to the final as the top qualifier .
The Aucklander had arrived in Berlin as an overwhelming favourite for the title.
She had recorded the best seven throws of this year, including her personal best of 20.69m, posted in Brazil in May.
Vili is the first New Zealander to retain a world athletics championships title.
The only other New Zealander to win a gold medal at this level was discus thrower Beatrice Faumuina in 1997.
