Md. Const. art. I, § 12

Except as otherwise specifically provided herein, a person is ineligible to enter upon the duties of, or to continue to serve in, an elective office created by or pursuant to the provisions of this Constitution if the person was not a registered voter in this State on the date of the person’s election or appointment to that term or if, at any time thereafter and prior to completion of the term, the person ceases to be a registered voter.