Jackie Fairweather (née Gallagher; born 10 November 1967) is a World Champion Australian triathlete and long-distance runner. Fairweather began competing in triathlon in 1992, and won the elite Australian National Series in her first season. She spent eight years as a professional triathlete and in 1996 she became ITU World Triathlon Champion in Cleveland, Ohio, setting a championship record time of 1 hour 50 minutes 52 seconds. She also won the ITU World Duathlon Championships in 1996 to become the only person ever to win both world titles in the same year.

Fairweather won the ITU Duathlon World Championships again in 1999, but narrowly missed repeating the double in the Triathlon World Championship, after finishing 2nd to Loretta Harrop. Fairweather collected further World Championship silver medals in 1995 and 1997, and won the bronze medal in the marathon in the 2002 Commonwealth Games (after finishing 11th in her first ever marathon in Boston).

Fairweather was known for her analytical approach to the sport and tenacity to try something different, the two contributions she is most proud of reflect that. One was her role in helping establish the Junior and Under23 World Championship format, with clear age divisions and a sprint distance for juniors.

In 2004, she married the Australian Olympic archery champion Simon Fairweather. She was also the inaugural coach of the Australian Institute of Sport (AIS) Triathlon program between 2001 and 2005.