Mazepin was born in Moscow and raised in Russia. He studied international relations at the Faculty of Global Studies at Moscow State University, graduating with a bachelor's degree in 2021 and a master's degree in 2023. He also completed a reserve officer training program at the university's military training centre, attaining the rank of lieutenant in the reserve of the Russian Armed Forces.
Mazepin began competing internationally in karting in 2011 and progressed rapidly through the CIK-FIA ranks. In 2014, his final karting year, he finished second in the Karting World Championship to Lando Norris.
After a brief appearance in the MRF Challenge Formula 2000 and the Toyota Racing Series at the end of 2014, Mazepin joined the Formula Renault 2.0 Eurocup in 2015, competing for Josef Kaufmann Racing alongside Louis Delétraz and Dries Vanthoor. He scored one podium that season, finishing third at the Red Bull Ring.
Mazepin entered the FIA Formula 3 European Championship in 2016 with Hitech Grand Prix. His season was overshadowed by a physical altercation with Callum Ilott following a blocking incident, which resulted in a ban from the first race at the Hungaroring. He finished 20th, last among full-time entrants.
He was retained for 2017 and improved considerably, scoring 108 points, three podiums, and finishing tenth.
Mazepin moved to the GP3 Series in 2018 with ART Grand Prix, partnering Callum Ilott among others. He won four races — more than any other driver that year — and finished runner-up in the championship, sixteen points behind champion Anthoine Hubert. His performances also helped ART clinch the teams' title.
Mazepin graduated to Formula 2 in 2019 with ART Grand Prix alongside championship winner Nyck de Vries. He ended the season in 18th with eleven points, his campaign marked by causing an accident with Nobuharu Matsushita in Sochi.
In 2020, he joined the new Hitech Grand Prix team alongside Luca Ghiotto. He took his first podium at the Hungaroring and won two feature races — at Britain and Mugello — ending the season fifth overall.
Mazepin signed a multi-year deal with Haas for 2021, partnering Mick Schumacher. He chose the number 9 and competed under a neutral flag representing the Russian Automobile Federation, following the CAS ruling upholding a WADA ban on Russia at World Championships due to state-sponsored doping.
His debut at the Bahrain Grand Prix ended immediately when he crashed out on the first lap after losing control on a kerb. The season saw multiple incidents, including a five-second penalty for blocking Sergio Pérez during the Portuguese Grand Prix while ignoring blue flags. His best result — fourteenth — came at the Azerbaijan Grand Prix, largely due to retirements elsewhere on the grid. Mazepin missed the Abu Dhabi finale after testing positive for COVID-19 and was not replaced. He finished 21st in the championship without scoring a point.
A test driver for Force India from 2016 to 2018, he had also impressed in 2019 when he topped the timing sheets at the Barcelona in-season test for Mercedes, driving the W10.
Haas terminated Mazepin's contract on 5 March 2022, three days after Russia's invasion of Ukraine, simultaneously ending Uralkali's title sponsorship. Mazepin described the decision as "cancel culture" in a BBC interview and expressed willingness to continue racing under whatever conditions were proposed, stating those terms were "completely ignored."
In July 2022, Mazepin sued Haas in a Swiss court for unpaid wages. A prolonged legal battle followed, with Haas's assets seized at the 2024 Dutch Grand Prix during proceedings with Uralkali. Mazepin and his father were placed on EU, UK, and Canadian sanctions lists in March 2022. EU sanctions against Nikita personally were lifted in March 2024 after the Court of Justice of the European Union found the "association" criterion was not sufficiently established by the Council.
Following his F1 exit, Mazepin founded 99 Racing, a Jordanian-British sportscar team. He competed in the Asian Le Mans Series with the team from 2023 to 2024, winning multiple races including a podium at the opening round in Dubai with Neel Jani and Gonçalo Gomes.
In rally raid, Mazepin won his T3 class at the Silk Way Rally in 2022, and earned a Master of Sports of Russia recognition in May 2025. In 2025, he joined the Middle East Trophy driving for Graff Racing.
In December 2020, before his F1 debut, Mazepin posted an Instagram story showing him appearing to grope a woman's breasts. Haas described the video as "abhorrent" and Mazepin issued an apology, though he later deleted it. The incident generated significant public backlash and the trending hashtag "#WeSayNoToMazepin."