Mont. Code Ann. § 37-61-416

A party to a civil action who is of legal age may prosecute or defend the action in person or by attorney at the party's election unless the party has been judicially declared to be incompetent to manage the party's affairs. Each provision of this part relating to the conduct of an action in which the attorney for the party is mentioned includes a party prosecuting or defending in person unless otherwise specially prescribed or unless that construction is manifestly repugnant to the context. If a party has an attorney in the action, the party may not appear or act in person when an attorney may appear or act either by special provisions of law or by the course and practice of the court.