Demir started playing football with his local club Mersin at the age of 6, and moved to Kayserispor 2 years later.

[2] One week after his 15th birthday, Demir made his professional debut with Kayserispor in a 0-0 Turkish Cup tie with Akhisarspor on 22 January 2019, playing the final three minutes of the match.

[3] On 9 November 2019, aged 15 years and 299 days, he became the youngest goalscorer in Süper Lig history when he scored against Gençlerbirliği.

[4] On 23 September 2021, Barcelona Atlètic announced an agreement with Kayserispor to sign Demir for the 2022–23 season for a fee of 2 million euros.

[6][7] Having not managed to break through Barcelona's team consistently, on 31 January 2023 Demir returned to Turkey, joining Süper Lig club Fenerbahçe on a free transfer and signing a four-and-a-half-year deal.