[4][5] He then joined Haderslev Fodboldklub before the name was changed to HFK Sønderjylland and SønderjyskE and signed his first professional contract with the club, keeping him until 2003.

[8] In 2001, Poulsen was quickly promoted to the club's first team and scored on his debut, in a 4–2 win against FC Aarhus in the third round of the Danish Cup.

[17] His performance attracted interest from Bundesliga side Werder Bremen, who offered him a trial, but Poulsen ended up staying at the club.

[21] Amid to his departure, Poulsen made five times for SønderjyskE at the start of the 2005–06 season, including scoring his first Danish Superliga goal, in a 3–1 loss against Viborg on 7 August 2005.

[28] Poulsen then played in both legs in the first round of the UEFA Cup, as FC Midtjylland lost 6–2 against CSKA Moscow on aggregate and was eliminated from the tournament.

[30] On 4 May 2006, Poulsen returned to the first team, starting a match and played 77 minutes before being substituted, in a 1–0 win against Odense BK.

[54] On 31 August 2008, he made his first appearance of the season for AZ Alkmaar, starting a match and played 60 minutes before being substituted, in a 2–1 loss against NAC Breda.

Ahead of the 2009–10 season, it was expected that Poulsen would leave AZ Alkmaar, due to lack of first team opportunities, but ended up staying at the club.

[64] Three days later on 29 September 2009, Poulsen made his UEFA Champions League debut, coming on as a 71st-minute substitute, in a 1–1 draw against Standard Liège.

[72] But he made his return to the starting line–up in a UEFA Europa League match against Sheriff Tiraspol on 16 September 2010, coming on as a second-half substitute, in a 2–1 win.

[80] He started the season well for AZ Alkmaar by helping the club qualify for the Group Stage of the UEFA Europa League after beating the likes of Jablonec and Aalesunds.

[81] Poulsen then helped AZ Alkmaar keep three consecutive clean sheets in three league matches between 21 August 2011 and 10 September 2011.

[83] Between 23 October 2011 and 25 November 2011, Poulsen, once again, helped AZ Alkmaar keep four consecutive clean sheets in four league matches.

[85] Five days later on 15 December 2011, Poulsen helped the club qualify for the knockout stage of the UEFA Europa League after drawing 1–1 against Metalist Kharkiv.

[99] Since joining the club, however, Poulsen found his first team opportunities limited at Sampdoria, due to strong competitions in the defence.

[104] On the same day when his contract with Sampdoria had been dissolved on 16 January 2014, Poulsen rejoined his former team AZ Alkmaar, keeping him until 2015.

[106] Poulsen made his AZ Alkmaar debut on 8 February 2014, coming on as a 73rd-minute substitute, in a 2–1 loss against Go Ahead Eagles.

[120] Poulsen returned to the starting line–up against Ajax and set up the only goal of the game to help AZ Alkmaar win 1–0 on 5 February 2015.

[126] A month later on 19 September 2015, Poulsen made his league debut for the club, coming on as an 80th-minute substitute, in a 2–1 loss against Heracles Almelo.

[128] However, throughout the 2015–16 season, Poulsen found himself placed on the substitute bench, as he was as cover for incumbent PSV left-back Jetro Willems.

[131] In the 2016–17 season, Poulsen's first team opportunities at PSV Eindhoven continued to be limited, covering for Willems and made no appearances for the club.

[139] After missing the next three matches due to quarantine, he returned to the starting line–up against Brøndby on 21 May 2017 and helped the club keep a clean sheet, in a 3–0 win.

[156] In a follow–up match, Poulsen captained SønderjyskE for the first time this season in the absence of Pedersen and helped the club draw 1–1 against Hobro.

[170] Initially not getting playing time against Spain, he made his national team debut in a friendly match against Germany on 28 March 2007, coming on as a substitute for Dennis Rommedahl, in a 1–0 win.

[172] Following this, his international career went on a hiatus and it wasn't until on 10 May 2010 when Poulsen was recalled to the team, ahead of the 2010 FIFA World Cup, as Olsen thought he had improved in the back position.

[175] On 14 June in their first 2010 FIFA World Cup group match against the Netherlands, Poulsen had a crucial part in Daniel Agger's own goal by heading the ball against his back inside the first minute of the second half which deflected past the Danish goalkeeper, thus giving the Dutch the lead, and the national side went on to lose 2–0.

[179] Poulsen was featured against England on 9 February 2011 and was at fault for conceding an equalising, leading him to be substituted at half time, as Denmark lost 2–1.

"[184] He then featured two more matches in the tournament for the national team, playing in the left–back position against Portugal and Germany, as they were eliminated in the group stage.

[186] He made his first appearance in nine months against Czech Republic on 22 March 2013 and started the whole game to help the national team keep a clean sheet, in a 3–0 win.

[195] The combination of his daughter being born and scoring against Go Ahead Eagles on 21 February 2015 led Poulsen to describe the week as "fantastic".