[11] Axelsen held the world number one position in men's singles for a total of 183 weeks, making it the third-longest reign in badminton history, trailing only Lee Chong Wei (398) and Lin Dan (211).

[17] He made his debut in the senior international tournament at the 2009 Denmark Open playing in the men's doubles event with Steffen Rasmussen.

[13] In January 2010, Axelsen who played from the qualification round, manage to reach the finals at the Swedish International tournament, and finished as the runner-up after losing to Indra Bagus Ade Chandra in straight games 15–21, 12–21.

[18] He competed at the World Junior Championships in Guadalajara, Mexico, claimed the boys' singles title by defeating the No.1 seed, China's Huang Yuxiang in the quarter-finals, India's B. Sai Praneeth in the semis and Kang Ji-wook of Korea in the final.

[19] A few weeks later he entered his first Super Series event in singles, the 2010 Denmark Open; making it through the qualifying stages before losing out to compatriot and eventual winner Jan Ø. Jørgensen in the second round.

[21] He took a silver medal at the 2011 BWF World Junior Championships, losing the title to Malaysia's Zulfadli Zulkiffli, coming in second place.

[31] Axelsen followed up his victory in Glasgow by winning the finals of the Japan Open tournament in Tokyo over Lee Chong Wei of Malaysia in three sets on 23 September, propelling him to the top of the BWF World Rankings.

[34] In February, he managed to defend his title in the Barcelona Spain Masters after beating the Thai youngster Kunlavut Vitidsarn in straight games 21–16, 21–13.

[40] In October, he won the Denmark Open title, defeating the top seed and world no.1 Kento Momota in a thrilling final match in three games.

[52] On July 3, Axelsen won the Malaysia Open for the first time by defeating Kento Momota 21–4, 21–7 in the final, becoming the first Dane to win the event in 15 years.

Subsequently, Axelsen participated in the Indian Open, a Super 750 event, where he encountered minimal resistance en route to the final.

In the All England Open tournament held in March, Axelsen faced an upset exit in the second round, losing to unseeded Ng Tze Yong in a closely contested three-game match.

However, Denmark suffered a 1-3 loss to Malaysia, with Axelsen sustaining a left hamstring injury during the first game against Lee Zii Jia.

[62] Later in the same month, despite just recovering from his injury, Axelsen participated in the Indonesia Open, a Super 1000 event, in which he successfully defended his title by overcoming opponents Weng Hongyang, Wang Tzu-wei, Chou Tien-chen, and the second-seeded local favorite Anthony Sinisuka Ginting.

Moving to July, Axelsen secured a significant victory by winning the European Games men's singles title for the first time.

Axelsen achieved this feat by defeating opponents Lin Chun-yi, Chico Aura Dwi Wardoyo, Prannoy H. S., Kodai Naraoka, and the fifth-seeded Jonatan Christie.

In the French Open, Axelsen faced another setback, retiring prematurely in the first round against Ng Ka Long due to injury.

This Super 500 tournament featured the participation of all top 10 players, and Axelsen's victory propelled him to the fifth position in the race to the World Tour Finals, securing his eligibility for the event.

Advancing to the final, Axelsen faced Shi Yuqi once again, overcoming an earlier defeat and the strong support of the host nation for his opponent.

In a remarkable achievement, Axelsen secured his third consecutive World Tour Finals title, a feat previously accomplished only by Lee Chong Wei.

[64] Participating in the inaugural tournament of the season Malaysia Open, Axelsen advanced to the semi-finals after defeating Loh Kean Yew, Lee Cheuk Yiu, Ng Ka Long, respectively.

In the Thomas Cup, his Denmark team lost 1–3 to Chinese Taipei in the quarter-finals, in which Axelsen was defeated by Chou Tien-chen in three games.

In the Malaysia Masters, Axelsen reached the final without dropping a game against Koki Watanabe, Panitchaphon Teeraratsakul, Chou Tien-chen, and Lu Guangzu.

In the following tournament, Singapore Open, Axelsen withdrew ahead of the semi-final match against the sixth seed Li Shifeng, citing "a small rollover" on the right ankle.

This included withdrawing from Indonesia Open, where he was the defending champion, thus forfeiting 12,000 points and losing his world number one ranking to Shi Yuqi for the first time since December 2021, ending a 132-week tenure.

Entering the Paris Olympics as the second seed, Axelsen advanced effortlessly through the group stage with straight wins against unseeded players Prince Dahal, Misha Zilberman, and Nhat Nguyen.

Benefiting from a favorable knockout stage draw, he received a bye to the quarter-finals, where he overcame the tenth seed Loh Kean Yew.

Despite Vitidsarn's impressive performance leading up to the final, Axelsen secured a commanding victory with scores of 21–11, 21–11, thereby successfully defending his Olympics gold medal.

In the month following his Olympic gold medal in Paris, he competed in the Hong Kong Open, marking his return to BWF Tour.

This makes it more comfortable in Asia than in Europe, especially Denmark, which tends to be cooler and where his allergy can be triggered faster by things such as flower pollen, dust, or animal dander.