In the video posted on YouTube, Cantlie, wearing an orange jumpsuit, speaks to the camera in the style of a news report and promises to reveal in a series of programmes the "truth" about the jihadist group that has seized parts of Iraq and Syria.
There was no immediate threat to his life apparent in the video.
Cantlie, who had contributed to British newspapers including The Sunday Times and Sunday Telegraph, as well as to Agence France-Presse, said he was captured after travelling to Syria in November 2012.
He had previously been detained along with a Dutch photographer by extremists in Syria in July 2012 but was reportedly released after nine days.
It was not clear when the video was shot, but in it Cantlie referred to recent events including IS taking control of large parts of Iraq in June.
Speaking in English with Arabic subtitles, Cantlie says in the 3:21-minute video -- titled "Lend Me Your Ears" -- that he plans to reveal "the truth behind the systems and motivation of the Islamic State".

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