Fairweather won bronze in the women's 800 meters freestyle in a time of 8:22.26 with teammate Eve Thomas taking fourth clocking 8:24.86.
Italy's Simona Quadarella completed the distance double in Doha with just .09 seconds separating her and silver medallist Isabel Gose from Germany.
Fairweather pushed the pace through the first half of the race to lead at the halfway mark, but she couldn't hold on to the leading duo in the back half of the race.
Earlier in the championships Fairweather, 20, sensationally won New Zealand's first ever world championships title in the 400 meters freestyle, and claimed silver in the 200 meters freestyle.
With the Paris Olympics approaching many of the world's top swimmers chose to skip the Doha championships to focus on building towards Paris.