Dabiq holds crucial ideological importance for IS because of a Sunni prophecy that states it will be the site of an end-of-times battle between Christian forces and Muslims.
The town itself has negligible military value compared with the strategic IS-controlled cities of Raqa in Syria and Mosul in Iraq.
The Syrian Observatory for Human Rights said rebels backed by Turkish warplanes and artillery "captured Dabiq after IS members withdrew from the area".
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Observatory head Rami Abdel Rahman said the fighters also captured the nearby town of Sawran.
One Turkey-backed rebel faction, the Fastaqim Union, also said Dabiq had fallen "after fierce clashes with Daesh," using the Arabic acronym for IS.
It published pictures on Twitter of a group of fighters on the back of a small white truck waving assault rifles in the air, with the town of Dabiq apparently in the background.
According to Turkey's state-run Anadolu news agency, the rebel fighters were working to dismantle mines laid in the town by retreating IS fighters.
Anadolu said nine Syrian rebels were killed and 28 others wounded during clashes on Saturday.