TPS Moisander started his football career together with his twin brother
Henrik, both joining local
TPS from their home town of
Turku in 2001. A year later, he made his debut in the
Veikkausliiga, the premier division of Football in Finland, under then manager
Mika Laurikainen. He was selected in the starting lineup on 15 May 2003 in a regular season's fixture against cross town rivals
Inter Turku. He played the full 90 minutes in the 2–0 away win in his first Turku derby match. He went on to make 17 appearances for TPS during the
2002 and
2003 seasons, becoming a regular with his home club at age 17.
Ajax On 5 June 2003, it was announced that Dutch
Eredivisie club
Ajax had signed the twins Henrik and Niklas to a two-year contract, binding them to the club until the summer of 2005. At Ajax, they would join the team where both
Finland Internationals
Jari Litmanen and
Petri Pasanen were playing at the time. At first instance, the twins were to join the under-19 team of
Ajax A1, competing in the 2003–04 A-junioren Eredivisie league in their first year with the club. The twins helped their side secure the club's eighth A-Juniors league title, under the tutelage and guidance of then coach
Danny Blind. The following season saw Moisander and his brother compete in the
Beloften Eredivisie for the team's reserve squad
Jong Ajax, where they would help to win the reserve league title in their first year on the team. Signing a contract extension for an additional year by the end of the season, Ajax eventually won the
KNVB Cup in conclusion. 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.
FC Zwolle On 3 May 2006 it was announced that Moisander would transfer to the
Eerste Divisie side FC Zwolle, signing a two-year contract with the club from
Overijssel. 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. Midway through his first season, his contract was annulled and extended for an additional year, binding him to the club until the summer of 2009. After his first two seasons, and with one year still remaining on his contract, Zwolle and
AZ Alkmaar agreed to terms for a direct transfer of Moisander for a reported €600,000 transfer fee, returning to the top flight of Dutch football. During his stay in Zwolle, he made 75 appearances for the club, scoring five times, where he was an instrumental player for his side.
AZ 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. He made his Eredivisie debut on 20 September 2008 for AZ in its 1–0 home win against Dutch giants
PSV. He scored his first goal for AZ on 3 October 2008 in the 6–0 regular season victory over
Sparta Rotterdam. 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. in 2011 Moisander quickly came back to help his side win the Eredivisie title, the second for the club in its history and Moisander's personal first. That season, the title race had come down to the final round, and although AZ had lost their last game of the season against
Vitesse, it was still able to consequently clinch the league due to eminent losses suffered by title contenders Ajax and
Twente. The following season, Moisander made his continental debut, playing in the
2009–10 UEFA Champions League group stage campaign. 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. This was after having won the Dutch Super Cup (the
Johan Cruyff Shield) against
Heerenveen at the start of the season. Midway through the season, the team changed management again when
Dick Advocaat was hired as a replacement for Koeman, and the club finishing the season in fifth place and thus qualifying for the
2010–11 UEFA Europa League Third qualifying round. Ahead of the 2010–11 season, AZ had found another replacement in
Gertjan Verbeek as the new manager. Moisander played a major role in helping his side to qualify for the
2010–11 Europa League group stage, having appeared in all four games in the qualifying rounds. He also played in four of the six group stage encounters against
Dynamo Kyiv,
BATE Borisov and
Sheriff Tiraspol. The team, however, finished the league in fourth place, thus qualifying for the qualifying rounds once more. Following the departure of
Stijn Schaars to
Sporting CP ahead of the 2011–12 season, Moisander was appointed as AZ's new
team captain. Securing the group stage of the
2011–12 Europa League once more, through a successful qualifying campaign against
Baumit Jablonec and
Aalesunds FK, his team would then successfully advance out of the group stage, where it faced off with the likes of
Austria Wien,
Malmö FF and
Metalist Kharkiv, finishing in second place in the group. The club then advanced to the quarter-finals by defeating
Anderlecht and
Udinese in previous rounds, eventually bowing out to
Valencia 5–2 on aggregate. Moisander played in 14 matches during the club's continental campaign, when it reached the quarter-finals of the competition for the fourth time in the club's history. Moisander started the
2012–13 Eredivisie season with AZ, making two league appearances, before transferring back to neighboring Ajax.
Return to Ajax 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. Moisander made his Eredivisie debut for Ajax on 25 August 2012 in a match against
NAC Breda, where he also scored a goal. He established himself as the first-choice centre back under manager
Frank de Boer, making a total of 29 league appearances in his first season back with the club while adding four goals. On 3 October 2012, he scored a header in a
UEFA Champions League match, a 4–1 home defeat against
Real Madrid. He then scored the winner in the Champions League game against
Manchester City on 24 October, again with a header. Moisander played in all six matches during the clubs'
2012–13 Champions League campaign, where the club finished in third place behind
Borussia Dortmund and Real Madrid, thus qualifying for the
2012–13 Europa League round of 16, where the team would suffer an early exit by a loss to
Steaua București, losing 4–2 on penalties in the final match following a 2–2 deadlock. Moisander was voted
Finnish Footballer of the Year by both the
Football Association of Finland and the Finnish Sports' Journalists Association, as Ajax went on to win its 32nd league title in his first year back with the club. 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. He played his 50th official match for Ajax on 22 September in the
Topper match against rivals PSV, which ended in a 4–0 loss for Ajax. 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. Moisander participated in the match for 60 minutes in order to regain his form after having suffered an injury which kept him sidelined for a month. Moisander was sent off against his former club AZ in a controversial decision. Ajax went on to lose the match 1–0.
Sampdoria On 25 March 2015, it was announced that Moisander would move to Italian
Serie A club
Sampdoria at the end of the 2014–15 season. As his contract at Ajax was expiring, he moved on a
free transfer, signing a three-year contract. He made his Serie A debut on 30 August 2015 in a match against
Napoli when he replaced
Éder as a substitute on 88th minute.
Werder Bremen On 9 July 2016, German
Bundesliga side
Werder Bremen announced it had completed the signing of Moisander. The transfer fee paid to Sampdoria was a reported €1.7 million. 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. On 8 July 2017, he suffered a torn muscle fibre in his right thigh playing in a friendly match against his former club Ajax Amsterdam, the match was later abandoned because Ajax player
Abdelhak Nouri suffered a heart attack. In July 2018, Moisander's contract was extended. In July 2019, he was announced as the club's captain after
Max Kruse's departure. After playing the first three league matches of the season, he suffered a thigh injury. In May 2021, Werder Bremen announced that Moisander's contract would not be extended.
Malmö FF On 1 July 2021, Moisander joined
Allsvenskan side
Malmö FF. He helped them win the
2021 Allsvenskan as well as the
2021–22 Svenska Cupen titles during his first year at the club. On 28 September 2023, Moisander extended his contract with Malmö, signing a new deal until the end of 2024. On 6 December 2024, after the
2024 Allsvenskan, Moisander announced his retirement from professional football. ==International career==