The "Defend the Guard Act" establishes that the Montana National Guard cannot be deployed to active combat duty without an official declaration of war or specific congressional action. The bill outlines that the Montana National Guard and its members may only be released into federal duty if the U.S. Congress has either passed an official declaration of war or taken action under Article I, section 8, clause 15 of the U.S. Constitution. The Governor of Montana is tasked with enforcing this provision, ensuring that the National Guard remains under state control unless these conditions are met.

Additionally, the bill clarifies the powers of the Governor regarding the Montana National Guard, allowing for activation for federally funded missions that remain under state control, such as training, responding to domestic emergencies, and homeland defense activities. The act does not restrict the Governor's authority to consent to these missions, nor does it prohibit constitutionally authorized missions under Title 10 of the U.S. Code, as long as they comply with the provisions of the act. The bill is set to take effect immediately upon passage and approval.