Nikolai Morilow made his international debut in December 2003 in the Continental Cup. At the Junior World Championships in 2004 in Stryn he won bronze over 10 kilometers and with the relay and was tenth in the sprint. In December 2004 Morilow was used for the first time in the World Cup in Bern . The sprint specialist finished 36th in the sprint and twelfth in the team sprint. At the Junior World Championships in 2005 in Rovaniemi , Finland , he was sixth in the sprint and 31st in the pursuit race over 2 × 10 kilometers. In the period that followed, the Russian commuted between the World Cup, FIS races and the Continental Cup. At the Junior World Championships in 2006 in Kranj , Slovenia , he was eighth in the sprint, tenth over ten kilometers in the classic style and twelfth in the pursuit over 2 × 10 kilometers.
At the beginning of the following season he won his first World Cup victory in a team sprint with Alexei Petuchow in Düsseldorf . In January 2010 he won the team sprint and the sprint race in Rybinsk . At the 2010 Winter Olympics in Vancouver , he came 26th in the sprint. Together with Petuchow he won the bronze medal in the team sprint. He finished the season in eighth place in the sprint classification. At the Nordic World Ski Championships in Oslo in 2011 , he came eighth in the sprint. He ran his best World Cup season in 2011/12 . He achieved placements in the top ten in eight out of ten sprint races. He got two second places in races in Rogla and Szklarska Poręba . In mid-January 2012 he won the team sprint in Milan together with Alexei Petuchow. At the Tour de Ski 2011/12 he won the sprint stage in Toblach . He finished the season in 15th place in the overall World Cup ranking and in second place in the sprint ranking. In January 2013 he and Mikhail Dewjatjarow won his last World Cup victory in the team sprint in Liberec . The following month he took his first victory in the Eastern Europe Cup in the sprint in Moscow . In the 2015/16 season he finished 13th in the overall ranking of the Eastern Europe Cup. He won the sprint in Moscow in February 2016.