2007-08: Jani Lajunen played with three different clubs this season, but all were within the Blues Espoo organization. He started with the U18 squad, and then moved up to the junior team. In 25 games he netted four goals and 10 assists before moving up to the senior squad for one game.
2008-09: Lajunen split time between the Blues in Finland's SM-liiga and their U20 junior team for most of the season. In 25 games with the junior club, the center scored 16 goals, 10 assists for 26 points. In 25 games with the big club, he scored 1 goal, 1 assists for 2 points. He played in 3 games with the Blues in the Champions Hockey League, scoring 1 goal. He was also loaned to the Suomi U20 team in Finland's second-tier league, where he scored 2 goals, 2 assists in 2 games. Lajunen also suited up for Finland at the WJC tournament, scoring 1 goal in 6 games.
2009-10: Lajunen spent the majority of his season with the Blues in the SM-liiga, scoring 6 goals with 9 assists in 46 games. He was held off the scoresheet in 3 postseason appearances. Lajunen also scored 1 goal with 1 assist in 4 games with the Blues U20 squad and had no points in 2 appearances on loan to Suomi's U20 team. He represented Finland at the 2010 U20 World Junior Championship after playing in the 2009 tournament and scored 1 goal with 4 assists for 5 in six games. Lajunen signed a three-year, entry-level contract with the Predators in May 2010.
2010-11: Lajunen skated in a career-high 60 games for the SM-Liiga's Espoo Blues as a 20-year-old. He scored 10 goals with 12 assists and was +7 with 46 PMs during a disappointing regular season. After finishing ninth in the 14-team league, Espoo made a surprise run to the SM-Liiga playoff finals before falling to HIFK Helsinki. In 18 playoff games Lajunen scored 3 goals with 4 assists and was -2 with 12 PMs. Lajunen was the second youngest player on Finland's gold medal-winning squad at the 2011 IIHF World Championship and scored 2 goals with 1 assist and was +2 with 2 PMs in four games.
2011-12: Originally signed by Nashville following the 2009-10 season, Lajunen skated for the Predators AHL affiliate Milwaukee in his first season in North America. Playing in mostly a lower line, checking role with the Admirals, he scored 5 goals with 11 assists in 75 games and was plus-five with 18 penalty minutes. After finishing second in the North Division, Milwaukee was swept by Abbotsford in the first round of the playoffs. Lajunen scored 1 goal and was plus-one in the three playoff games against the Heat.
Lajunen has a good skill set and offensive instincts. Very quick for his size, Lajunen is very good at anticipating plays and can get the puck to teammates very effectively.
Projects as a third liner with some offensive upside.
Lajunen was dealt by the Nashville Predators to the St. Louis Blues in March of 2013.