Lawrence, who competed for Wales at the 2014 Commonwealth Games, finished her swim, bike and run in a total time of four hours, nine minutes and 11 seconds on the Sunshine Coast.
The 26-year-old was nearly two minutes ahead of Australian two-time winner Melissa Hauschildt.
Fellow Welsh competitor Leanda Cave won the same title in 2012.
Swansea triathlete Holly Lawrence has won the women's half ironman 70.3 World Championship in Australia.