2012–2013

At the 2012 World Junior Championships, she reached the final in the 800 metres after running a personal best of 2:02.38 in her semi-final. The final was won by American Ajee' Wilson in a personal best of 2:00.91, with Nanyondo finishing a disappointing last in 2:07.23.

A year later, at the 2013 Summer Universiade in the 800 metres, her 2:02.96 finish time in the semi-finals was not fast enough to advance to the final. Nor did her 4:28.77 finish time in the semi-finals of the 1500 metres qualify her for the final.

2014

In 2014, Uganda hosted the Universiade World Cross Country Championships. Nanyondo took a 30-second victory to lead the home team to a 1-2-3 sweep and the team championship.^[2][3]

Later in the year, she improved her track performance, taking her 800 metres time under 2:00.00 with a 1:59.27 race-winning performance in the Golden Spike Ostrava meet.^[4]

A little more than a month later, at the Herculis meet in Monaco, she again improved her personal best in the 800 meters to 1:58.63, which placed her third behind second-place finisher and 2013 world champion Eunice Sum (1:57.92) and the winner Ajee' Wilson (1:57.67).^[5][6]

At the 2014 Commonwealth Games in Glasgow, Scotland, Nanyondo won a bronze medal for finishing third in the 800 metres final with a time of 2:01.38, just behind Sum of Kenya and Lynsey Sharp of Scotland.^[7]

2015–2016

In 2015 and 2016, she raced slower than her personal best in the 800 metres, failing to run faster than 2 minutes flat. She ran her season's best time of 2:01.97 at a race in Kortrijk, Belgium on 11 July 2015, finishing third.^[8][9] At the 2016 Olympic Games in Rio de Janeiro, she did not advance out of the first round of the 800 metres event, finishing sixth in heat #5 in a time of 2:02.77.

However, she improved her personal best at 1500 metres in Kawasaki, Japan, on 10 May 2015, finishing the race in 4:17.13.