Gridin has been taking part in competitions organized by the Fédération Internationale de Ski since 2007 . At the Junior World Championship in Mals in 2008 , he won bronze in the 20 km mass start race. He made his first World Cup race in December 2008 in La Clusaz , which he finished in 60th place in the 30 km mass start race. At the Tour de Ski 2008/09 he reached 47th place in the overall standings.
Gridin started for Bulgaria in 2013. In January 2014, he achieved 45th place in the 15 km mass start race in Szklarska Poręba , his best individual World Cup result to date. His best placings at the 2014 Winter Olympics in Sochi were 41st place in the 50 km mass start race and 19th place in the team sprint. In the 2013/14 season he won the Balkan Cup.