[6] The twins helped their side secure the club's eighth A-Juniors league title, under the tutelage and guidance of then coach Danny Blind.

Unable to break into the first team, however, after their second term with the reserves, the twins were separated; while Henrik was dispatched to Assyriska in Sweden, Niklas remained in the Netherlands, where he signed with FC Zwolle instead.

[9] He made his debut on 11 August 2006 in a 2–0 win at home against Fortuna Sittard in the KNVB Cup match, at which point he immediately establishing his position in the starting XI of the team.

[12] On 11 July 2008, it was announced that AZ had come to terms with Zwolle for the direct transfer of Moisander, signing a three-year contract to bind him to the club until the summer of 2011.

[16] He was able to establish himself as the first choice defender under manager Louis van Gaal, playing a total of 22 full league matches, having briefly been sidelined in the months of January and February due to a knee injury.

[19] Playing in five out of the six matches against the likes of Arsenal, Olympiacos and Standard Liège, AZ finished in the bottom of the group under newly appointed manager Ronald Koeman.

[26] On 21 August 2012, both clubs agreed to terms of a €4 million transfer fee to acquire Moisander, as he returned to Ajax on a three-year contract as a replacement for the Tottenham Hotspur-bound Jan Vertonghen.

[33] Following an injury to Siem de Jong the following season, and after the departure of vice-captain, fellow centre back Toby Alderweireld to Atlético Madrid, Moisander wore the captain's armband for the first time for Ajax in an away match against Groningen on 1 September 2013.

On 4 November, he made an appearance in the Eerste Divisie playing for the newly promoted reserve team Jong Ajax in its 3–2 away loss to Helmond Sport.

[41][42] He made his Bundesliga debut in a 4–1 loss against Borussia Mönchengladbach on 16 September 2016, replacing Fallou Diagne at half-time with Werder Bremen trailing 0–4.

[55] Moisander made his debut for Finland at youth level, playing for the under-15 squad at age 14 on 29 August 2000 in a friendly match against Sweden-15 in Hallstavik, Sweden.

[57] Moisander made his official debut for the senior team on 29 May 2008 when he was called up by head coach Stuart Baxter for a friendly match against Turkey at the age of 22, which was contested in Duisburg, Germany.

[58] In fall 2008 and spring 2009, Moisander was named for the Finland squad for the 2010 FIFA World Cup qualification matches, but remained as an unused substitute.

[59] He permanently solidified his position in the team after Baxter brought him in for the final 2010 World Cup qualifying group stage match against Russia.

The match ended in a 3–0 loss for the Finns at home, which inevitably cost them the second place in the group, which was then secured by the Russians, leading to their advancement in the tournament, with Finland therefore failing to qualify for the 2010 World Cup.

While playing a major role in the teams UEFA Euro 2012 ambitions, Finland finished fourth in its group behind the Netherlands, Sweden and Hungary, failing to qualify for the final tournament in Poland and Ukraine.

[62] The 2014 World Cup qualification process ended in a third-place group stage finish for Finland behind both Spain and France, which both secured placement in the final tournament.

[64] Moisander scored his second goal for the national team on 14 August 2013 on his old home turf Veritas Stadion in Turku in a match against Slovenia when he took Finland on a 1–0 lead in a 2–0 victory.