Johaug and compatriot Martin Johnsrud Sundby became the first Norwegians to win the Tour de Ski when they won the women's and men's competitions in the 2013–14 edition of the race.

That year she also enjoyed her most successful World Championship performance in Falun, where she took three gold medals: two in individual events (the 15km skiathlon and the 30km classic mass start) and one as part of the Norwegian women's team in the 4x5km relay.

[6][7][8] Johaug followed her World Championship success with her best-ever World Cup season in 2015–16, winning a second Tour de Ski by overturning a 39-second deficit to Ingvild Flugstad Østberg on the final stage to complete the climb up Alpe Cermis with a lead of 2 minutes 21 seconds over runner-up Østberg.

[13] Johaug served an 18-month competition ban from October 2016 to April 2018 for an anti-doping rule violation after testing positive for unintentional use of clostebol.

[14][15] An initial suspension of 13-months was overturned and extended by the Court of Arbitration for Sport (CAS) following an appeal by the International Ski Federation (FIS).