The suspect was linked with a French IS cell that had planned to attack Paris on Thursday but was broken up by French authorities in November, the Moroccan interior ministry said.
The suspect had met IS operatives on the Syrian-Turkish border and received instructions to be delivered to the cell in France, it charged.
The orders came from the jihadist group in territory it controls in Syria and Iraq.
French security services broke up the cell by arresting seven men in Strasbourg and Marseille on November 19 and 20, according to the French interior ministry.
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A year ago, Moroccan intelligence helped put French investigators on the trail of Abdelhamid Abaaoud, a 28-year-old Belgian of Moroccan origin who had appeared in grisly IS videos and was linked to a series of plots in Europe.
A study by the US-based Soufan Group said last December that at least 1,200 Moroccans had travelled to fight alongside IS in Iraq and Syria in the previous 18 months.
Morocco has also arrested eight men with alleged ties to IS active in the cities of Fez and Tangiers, the interior ministry said yesterday.