Spokesman Murad Adayleh says the Islamic Action Front's leadership voted overwhelmingly late today to compete in the elections.
He says the IAF, the most organized opposition group in Jordan, will look for partnerships to improve its chances.
The Muslim Brotherhood in the kingdom started out as a branch of a region-wide movement, but suffered a series of splits.
The Muslim Brotherhood was declared illegal though its political arm was not after a group of defectors registered a new Muslim Brotherhood Society as a Jordanian entity.