Born in Middelfart, Denmark, Eriksen started playing football in his hometown before his third birthday. In 2005, he joined Odense Boldklub who competed in the Danish youth championships. In his debut season, OB lost in the semi-final against Brøndby IF but Eriksen was named "Best Technical Player" at the end of the tournament. The following year OB won the tournament, with Eriksen scoring the only goal in the final. After performing well for OB's U-16 team and later for the U-19 team and Danish U-17 team, major European football clubs including Chelsea and Barcelona were credited with an interest in Eriksen. The player had trials with Barcelona, Chelsea, Real Madrid, Manchester United and Milan, but finally decided to move to Ajax, stating, "My first step should not be too big. I knew that playing in the Netherlands would be very good for my development. Then Ajax arrived and that was a fantastic option."

Eriksen was called up to the Denmark national under-17 football team in July 2007, and impressed in his debut for the team on 31 July. In 2008, he scored nine goals in 16 games for the U-17s, and was named Danish U-17 Talent of the Year by the Danish FA. He was also one of four nominees for the 2008 Danish Talent of the Year award, which was won by Mathias Jørgensen. He played 27 games for the under-17 team until February 2009. He played a total of eight games for the Denmark U-18 and Denmark U-19 teams during 2009. Eriksen was also called up for the Danish U-21 squad to the European championship in Denmark in 2011, the Danish team only participated in the group stage and Eriksen scored a goal against Belarus.

On 17 October 2008, it was announced that Eriksen had signed a two-and-a-half-year contract with Amsterdam-based Ajax. The transfer fee received by OB was estimated at €1 million (£847,199). He worked his way through the youth teams, and was promoted to the first team squad in January 2010, where he was given the number 51 shirt. Within the month, he made his first team debut for the Dutch team in the Eredivisie on 17 January 2010 against NAC Breda. Ajax manager Martin Jol compared him to the likes of Ajax youth products Wesley Sneijder and Rafael van der Vaart and described him as a good reader of the game in the traditional "number 10" role like the two Dutch internationals and Danish legend Michael Laudrup, who also played for Ajax.

On 28 May 2010, Denmark coach Morten Olsen announced that Eriksen would be part of the final squad of 23 participating in the 2010 FIFA World Cup in South Africa. He was the youngest player participating in the tournament. At the World Cup, Eriksen played two matches, against the Netherlands and Japan, but Denmark were unable to progress beyond the group stage.

On 9 February 2011, in a 2–1 friendly loss at home against England, Eriksen was named Man of the Match, and was praised for his performance by a number of prominent footballing figures, including Chelsea star Frank Lampard, Man Utd star Rio Ferdinand (on Twitter), manager Morten Olsen and several media experts in Denmark and England. On 4 June 2011, Eriksen scored his first national team goal to give Denmark a 2–0 lead over Iceland in their Euro 2012 qualifier. In doing so, he became the youngest Danish player ever to score a goal in European qualification, being nine days younger than Michael Laudrup when he scored his first goal in 1983.

On 30 August 2013, Premier League club Tottenham Hotspur announced that they had completed the transfer of Eriksen from Ajax in a deal believed to be worth £11 million ($12.45 million). Eriksen joined the club on the same day as Érik Lamela, who joined from Roma, and Vlad Chiricheș, who joined from Steaua București, and took the club's total spending for the 2013 summer transfer window to £109.5 million. He made his league debut against Norwich City on 14 September 2013 and provided an assist for Gylfi Sigurðsson in a 2–0 victory. After the match, Spurs manager André Villas-Boas commented, "It was a great debut for Christian, he is a pure number 10, a creative player and his individual quality made all the difference."

Five days later, Eriksen "clipped a wonderful dipping shot" over the goalkeeper to score his first Tottenham goal and complete a 3–0 win over Tromsø IL in the Europa League. He added to his Tottenham goal tally with a goal from a free kick in a 1–1 draw against West Bromwich Albion on Boxing Day 2013, and the second goal in Spurs' 1–2 away win against Manchester United on 1 January 2014. On 23 March, after goals from Jay Rodriguez and Adam Lallana had given Southampton a 2–0 lead against Tottenham at White Hart Lane, Eriksen scored twice to level the score and assisted Sigurðsson to score the winning goal. He continued his goalscoring form on 12 April 2014 when he scored a stoppage-time equaliser to help Tottenham come from 3–0 down to draw 3–3 at West Brom. By the end of the season, he had scored ten goals and registered 13 assists across all competitions, won the Danish Football Player of the Year award and was named Tottenham's Player of the Season.

On 9 June 2015, amid speculation that he would be joining Manchester United, Eriksen confirmed to Danish media whilst on international duty that he would stay at Tottenham for the foreseeable Future and was quoted as saying, "I feel right at home at Tottenham and I haven't thought about leaving yet." He did in fact remain with the club and scored his first goals of the season in October, netting from two free-kicks in a 2–2 draw with Swansea.

In January 2016, Eriksen was once again named Danish Footballer of the Year. In doing so he became the first ever player to win the award in three consecutive years. He ultimately scored 6 goals and registered 13 assists as Tottenham ended the league season in third place, thereby qualifying for the following season's Champions League campaign.

Eriksen broke the record for the most goals scored by a Danish player in the Premier League when he scored his 33rd goal in a 3–2 win over West Ham on 23 September 2017, surpassing the record previously held by Nicklas Bendtner. On 9 December, he made his 200th career appearance for Tottenham and marked the occasion by scoring in a 5–1 Premier League win over Stoke City. The following month, he scored his 50th goal for the club when he netted after just 11 seconds in the 2–0 league win over Manchester United. Eriksen's goal was the third-fastest goal ever scored in the Premier League era, bettered only by Alan Shearer and former Spurs captain Ledley King. On 17 March 2018, Eriksen scored twice in an FA Cup fixture against Swansea City to send Spurs to the semi-final for the second season running. On 1 April 2018, Ericksen scored a 25-yard goal in the away match against Chelsea, helping Tottenham to their first win in 28 years at Stamford Bridge in a match that finished 3–1. Later that month, in the reverse fixture against Stoke, Eriksen scored twice to earn Tottenham a 2–1 win. Following the match, however, teammate Harry Kane, who was challenging for the season's Golden Boot award, claimed to have made the last touch on the ball for the second goal. Tottenham appealed to the Premier League panel who agreed that the ball touched Kane's shoulder and awarded him the goal.

In the build-up to the 2018 FIFA World Cup, Denmark were drawn in UEFA Group E alongside the likes of Poland and Romania. Eriksen played a key-role during the nation's qualification campaign during which time he scored eight goals to earn Denmark a play-off against the Republic of Ireland. The first leg of the play-off ended in a 0–0 home draw before Eriksen netted a hat-trick in Dublin's Aviva Stadium in a 5–1 win to earn Denmark a spot at the World Cup. Eriksen's treble took his tally to 11 goals for the qualification campaign, bettered only by Poland's Robert Lewandowski (16) and Portugal's Cristiano Ronaldo (15) in Europe, and earned the praise of national team manager Age Hareide who stated that Eriksen was one of the top 10 players in the world.