The Jury Act, at 28 U.S.C. § 1863(b)(6), lists those who are exempt from jury service. The following persons are legally barred from serving, even if they express a desire to serve.
Members in active service in the Armed Forces
Members employed full-time in active service in the Armed Forces of the United States. This is defined in 10 U.S.C. § 101(4) as including only the Army, Navy, Air Force, Marine Corps, and Coast Guard.
Note: A member of a National Guard unit is only exempt when called to active federal, as opposed to state, service. The individual must be a full-time, active-status member of a National Guard unit that is federally recognized, that constitutes a reserve component of a branch of the armed forces, as defined above, and that has been called into active federal service.
Members of fire or police departments
Members of fire or police departments, employed on a full-time basis, of any State, the District of Columbia, any territory or possession of the United States, or any subdivision of a State, the District of Columbia, or such territory or possession. Under this definition, members of federal law enforcement entities like the F.B.I., U.S. Customs and Border Protection, and the U.S. Marshals Service are NOT exempt from jury duty.
Note: A plain language interpretation of "police officer," for example, embraces the concept of someone charged with day-to-day maintenance of order throughout the community - a definition which generally would not include probation officers, court security officers, and so forth.
Public officers employed on a full-time basis who are either elected to public office or directly appointed by a person elected to public office in the executive, legislative, or judicial branches of the Government of the United States, or of any State, the District of Columbia, any territory or possession of the United States, or any subdivision of a State, the District of Columbia, or such territory or possession, who are actively engaged in the performance of official duties. 28 U.S.C. § 1869(i)
Note: The legislative history of the Jury Act indicates that the term “public officer” was intended to include only those persons whose government service is such that an interruption for jury duty would not be in furtherance of the public interest - usually persons with law- and/or policy-making functions.