Wiktionary
conspiracist
n. A person who puts forward a conspiracy theory.
Usage examples of "conspiracist".
When Phil O'Halloran, a freelance journalist, attempted to ask the ATF Public Relations Bureau why a Dipole Might expert just happened to be in the courthouse at that moment, and how he could immediately have known the exact nature of the bomb, O'Halloran, rather than given a rational explanation, was accused of attacking the agency and was promised a fax of agency views on Right-wing conspiracists (which never arrived).
A large number of the government conspiracists wanted Sarah Connor to have been abducted by aliens.