Tunçelli broke his first record at the age of 14, with a time of 15:05.25 in the 1500 m freestyle at the Turkey Turkcell Short Course Junior Individual Swimming Championship held in Istanbul.

In April 2023, at the Turkish National Team Trials for the Olympics held in Edirne, Tunçelli became the first swimmer 15 years old or under, with a time under 15 minutes for the 1500-meter freestyle event in the world.

In September, he came first in both the 800m and 1500m freestyle races at the 2023 World Aquatics Junior Swimming Championships, held in Netanya, Israel.

[11] In July 2024, he won the gold medal in both the 800-meter and 1500-meter freestyle at the Junior European Swimming Championships, setting a WJR in the 1500-meter [12] as well as leading his team of Eren Kuru, Ahmet Burak Işık, and Tuncer Berk Ertürk to a bronze in the 4 x 200-meter freestyle relay.

[13] At the 2024 Summer Olympics held in Paris, Tunçelli came second in his heat with a time of 7:47.29 in the 800m freestyle on July 29.

[15] Tunçelli, who finished the 1500m freestyle final on August 4th in the Olympics in 5th place, improved his own "World Junior Record" by 67 milliseconds with a time of 14:41.22.