[10] During the 2008–2009 season, Sotnikova debuted at the senior level at the 2009 Russian Nationals and won the gold medal at the age of 12.

[15] She struggled with a growth spurt and dropped to fourth at Russian senior nationals and sixth in the junior event.

[17] She was assigned to the World Junior Championships where she won the gold medal ahead of teammate Elizaveta Tuktamysheva.

She intended to begin her season at the 2011 Ondrej Nepela Memorial but withdrew after a leg injury caused her to miss a month of off-season training.

At the 2012 World Junior Championships, she won the bronze medal behind teammate Yulia Lipnitskaya and U.S. skater Gracie Gold.

In her next event, the 2013 Trophée Éric Bompard, she placed third in the short, first in the free skate, and won the silver medal behind American Ashley Wagner.

At the 2014 Russian Championships, Sotnikova placed first in the short, second in the free, and won her fourth national title, edging out Yulia Lipnitskaya for the gold.

Appearing in her second European Championships, Sotnikova placed first in the short and second in the free, taking the silver medal with an overall score of 202.36 points while Lipnitskaya won gold.

[12][26] Sotnikova won the gold medal in the ladies' individual event with an overall score of 224.59 points, becoming one of the youngest Olympic figure skating champions.

Sotnikova was selected to compete at 2014 Rostelecom Cup and 2014 NHK Trophy,[38] but withdrew due to a torn ankle ligament.

[41] While doctors had forbidden her to jump in full force,[42] Adelina Sotnikova decided to focus on the choreographic component in appearances with Gleb Savchenko[43] in the 2015 Russian version of Dancing with the Stars.

She appeared at two Challenger Series events, winning the silver medal at the 2015 Mordovian Ornament behind Anna Pogorilaya and placing 6th at the 2015 Golden Spin of Zagreb.

On the ISU Grand Prix, Sotnikova competed only at 2015 Rostelecom Cup, and won bronze medal behind her teammates Elena Radionova and Evgenia Medvedeva.

However, just prior to the 2019 Rostelecom Cup exhibition gala, her spine pain persisted to the point she was considering consulting for further treatment.

In December, after facing more serious pain, she was recommended surgery, but decided to delay it due to ongoing commitments, including performances of Plushenko's New Year show as Cinderella.

In late February, she underwent surgery, in which she got two spinal implants connected by a metal sheet, itself fixed by six titanium screws inserted into the vertebrae.

In July 2023, Sotnikova admitted in an interview she returned a positive doping test during the year of her Olympic triumph, but insisted she was cleared by her B-sample.

Sotnikova was named in the WADA-commissioned McLaren Report in December 2016 as one athlete about whom scratches indicative of tampering were found on test tubes in which urine samples were submitted, but the International Olympic Committee (IOC) cleared her of wrongdoing in November 2017 after deeming "there is no sufficient element in the evidence available to date" to establish an anti-doping rule violation.

Former Moscow laboratory director turned whistleblower Grigory Rodchenkov, the main witness in the McLaren Report, said she was not part of the programme.

[12] Sotnikova credits Maria as the most influential person on her career and sees figure skating as a job to support her sister.