In 2001, Sergey Ustiugov started practicing cross-country skiing in the biathlon section of the sports school of Mezhdurechensky.

[1][2] Ten years later he won gold in sprint at the World Youth Cross-Country Skiing Championships in Otepää, Estonia.

[3] A year later he became four-times champion of the Youth Championships in Erzurum, Turkey, in sprint, 10 km race, skiathlon and relay.

At the FIS Nordic World Ski Championships 2013 in Vale di Flemme, Ustiugov and his relay team claimed the bronze medal.

[7] In the 2015–16 WC season, in January 2015, he and Alexey Petukhov won the team sprint event at a World Cup stage in Otepää.

[11] He started the 2017 FIS Nordic World Ski Championships by winning the silver medal in the sprint competition.

However, between the Ruka Triple and the Tour de Ski, he rebounded and finished three times as runner-up in three different disciplines (sprint, individual, and pursuit).

[17] Prior to the Olympics, Ustiugov participated at the 50 km marathon event of the Ski Classics series in Cortina d'Ampezzo, finishing third.

[22] He returned to practice on 4 November,[23] and on 16 December he came back to sports in Davos, in the eighth stage of the new FIS World Cup season.

[24] In the 13th edition of the Tour de Ski, Ustiugov won the second stage in 15 km individual freestyle, exactly a year after his last victory.

In the third-last round, he got tired and fell behind the leaders, with his teammates Sobakarev, Larkov, and Vylegzhanin taking the lead.

While not winning a podium place this season, he qualified thrice to the sprint finals in Falun, Ulricehamn, and Oberstdorf.