Lankinen has played primarily for HIFK of the SM-liiga, from 2014 to 2018. He also played one match for Jokerit and two for KooKoo, and ten for Kiekko-Vantaa of Mestis. In 2014, Lankinen signed a three-year contract with HIFK. In the 2015 playoffs, he participated in the longest game in SM-liiga's history, lasting 134 minutes and 14 seconds. His team won 2–1 and advanced to the quarterfinals. During the 2015–16 season, Lankinen played alongside Ville Husso, playing 22 games in the regular season, as well as three in the playoffs as his team won silver medals. During the 2016–17 season, Lankinen was a secondary goaltender alongside the more experienced Niklas Bäckström, but due to Bäckström's injuries, he became the primary goaltender and played in 42 games, seven of which were shutouts, the most in the league that season. During the 2017–18 season, Lankinen was injured and unable to play for a large portion of the season. However, he made a successful comeback by playing 15 games in the regular season with four shutouts and a save percentage of 94.58 percent. His goals against average was 1.33, the highest in the league that season. During the playoffs, he played as the primary goaltender for 13 games with a save percentage of 93.56 percent, helping his team win bronze medals. He was in the running for the Urpo Ylönen trophy, which is awarded to the best goaltender of the season, alongside Veini Vehviläinen from Oulun Kärpät and Dominik Hrachovina from Tappara, but the award went to Vehviläinen. On 21 May 2018, Lankinen signed a two-year entry-level contract with the Chicago Blackhawks of the National Hockey League. In his second season with the Blackhawks affiliate, the Rockford IceHogs in the 2019–20 season, Lankinen made 21 appearances, earning 8 wins and represented the IceHogs as the teams' lone representative at the 2020 AHL All-Star Game. On 5 March 2020, Lankinen was ruled out for the remainder of the season after undergoing shoulder surgery, with a recovery period of 5 months.
International play
In 2019, Lankinen represented Finland in the Ice Hockey World Championships, winning gold. Throughout the tournament, he had the second highest save percentage of 94.20% and a goals against average of 1.50. He served as the goaltender for each playoff game.
