The 16-year-old’s success was backed up by a strong performance from her younger school colleague Annabel Denton, who finished seventh in the same event for Great Britain.
It was a terrific effort from the duo in extremely tough and unaccustomed conditions with basic facilities and the laser-run being held in sub-zero temperatures in the Kyrgyzstani capital.
The competition, run over two days, began with the swimming and fencing on Friday and the laser-run on Saturday.
Mitchell opened with a time of 2:17.64 for her 200m swim with Denton stopping the clock in 2:24.72.
The duo then moved to the fencing hall where Mitchell continued her fine 2017 form by recording 18 victories and 12 defeats from her 30 bouts, placing her fourth in the discipline standings.
Meanwhile, Dentonl, competing in just her fourth international competition and one of the youngest athletes in the field, recorded 13 victories from her 30 bouts.
It meant that they sat third and ninth after first day.
A thrilling laser-run followed with Mitchell overtaking the two athletes ahead of her before holding off the challenges of Egypt’s Mariam Amer and Kazakhstan’s Sofya Prizhennikova to take a stunning gold medal.
Like her older teammate, Denton also performed strongly in the final discipline, maintaining her form from last weekend’s British Modern Triathlon Championships to record the fifth quickest time in the laser-run and move up to seventh place at the competition’s conclusion.
The event provides valuable Youth Olympic Games World Ranking points for the British duo as the road to Buenos Aires 2018 continues.