"action or work of proselytizing," 1846, from proselytize + noun ending -ation.
1670s, "to make proselytes," from proselyte + -ize. The transitive sense of "convert (someone) to some religion, doctrine, etc.," is by 1796. Related: Proselytized; proselytizing. The earlier verb form was simply proselyte (1620s).