The 34-year-old former Watford and Sheffield United striker had been out of contract following his release by Coventry City in May.
Henderson has scored 129 goals in 486 career appearances, but failed to find the net in five substitute appearances for the Sky Blues last season.
Mansfield begin their EFL campaign away at Newport on Saturday, 6 August.
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League Two side Mansfield Town have signed experienced forward Darius Henderson on a free transfer.