The Collaborative International Dictionary of English v.0.48:

Ritualist \Rit"u*al*ist\, n. [CF. F. ritualiste.]
   One skilled un, or attached to, a ritual; one who advocates
   or practices ritualism.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ritualist
    n 1: an advocate of strict observance of ritualistic forms
    2: a social anthropologist who is expert on rites and ceremonies