
The National Intelligence Organization (MIT) said the suspect, whom it identified as Viskhan Soltamatov, was believed to be the key figure behind the Jan 28, 2024 attack.
He was detained by MIT and police during a joint operation in Istanbul, the agency said.
MIT said Soltamatov was also believed to have supplied the weapon used in the assault.
One Turkish citizen was killed by two IS gunmen at the Italian Santa Maria Catholic Church in Istanbul in January.
The church attack was orchestrated by IS-linked operatives from the Khorasan province (ISKP), a faction active in Afghanistan.
In April, Turkey had arrested 48 people believed to be linked to the attack.