Since his debut in 2001, he was a regular member of the Denmark national football team and played 92 matches, scoring six goals for his country.

[4] In September 2000, he underwent a trial period for Copenhagen in the top-flight Danish Superliga championship,[4] and signed his first professional contract with the club within a week.

After a change due to the release requirements by Copenhagen failed, Poulsen decided to play for Dortmund's arch-rivals Schalke 04.

His start in Schalke was made easier by the fact that his teammate in the Denmark national team, Ebbe Sand, also played for the club.

Through his time at Schalke, Poulsen played a number of matches at right back, but eventually secured himself a spot in the central midfield for both club and country.

In his debut match for the club, Poulsen helped Sevilla win the European Super Cup trophy, with a 3–0 victory against Barcelona on 25 August.

On 8 February, Poulsen scored his first goal for Juventus against Catania in the 90th minute, earning a win for his team after the game was heading for a 1–1 draw.

[13][14] On 19 August 2010, Poulsen made his debut against Turkish team Trabzonspor in the Europa League, in a match won by Liverpool 1–0, in which he had a goal disallowed.

On 20 November, he produced probably his best display in the centre of Liverpool's midfield against West Ham United at Anfield, a game which the home side won 3–0.

[16] Following the sacking of Roy Hodgson, and the appointment of new manager Kenny Dalglish, the winds changed not only for Liverpool but also for Poulsen.

[25] During his first season in Amsterdam, Poulsen was a regular in the starting lineup, helping his side to secure their third consecutive national championship, and Christian's first in twelve years.

On 14 May 2015, he set up the winning goal for Brandur Olsen in the Danish cup final as Copenhagen went on to beat FC Vestsjælland 3–2 after extra-time.

Following two yellow cards in the group stage, he was suspended when Denmark were eliminated in the knock-out phase by England.

Following the 0–0 draw with Italy, Danish television showed Poulsen being spat on by Italian playmaker Francesco Totti.

Totti received a three-match ban and gave a "full public apology", after failing in his claim that he was provoked by Poulsen.

[33] An aggressive, hard-working, and tactically versatile defensive midfielder, with good technique, Poulsen is known in particular for his tenacious tackling.