[1] Fernandez's first international competition was in 2012 when he competed at the Union Internationale de Pentathlon Moderne Youth World Championships in Hungary.

[4] In May 2014 Fernandez competed at the 2014 Union Internationale de Pentathlon Moderne International Junior Championships in Drzonkow, Poland, finishing 43rd in the individual event.

[4] In June 2015 Fernandez competed in the 2015 World Modern Pentathlon Championships and finished 12th in the men's relay event.

[4] On 18 July 2015 Fernandez won a gold medal at the 2015 Pan American Games in the men's individual event.

[7] At 19 years of age Fernandez became the youngest modern pentathlon gold medalist in the history of the Pan American Games.

[4] Fernandez won a gold medal at the 2016 Union Internationale de Pentathlon Moderne World Junior Championships in September 2016.

Fernandez was later appointed by IOC president, Thomas Bach, as an Athlete Role Model in the Youth Olympic Games held in Buenos Aires, Argentina, October 2018.