Justice Davis delivered the opinion of the Court:

On the 10th day of May, 1865, Lambden P. Milligan presented a petition to the Circuit Court of the United States for the District of Indiana, to be discharged from an alleged unlawful imprisonment...

Milligan insists that said military commission had no jurisdiction to try him upon the charges preferred, or upon any charges whatever; because he was a citizen of the United States and the State of Indiana, and had not been, since the commencement of the late Rebellion, a resident of any of the States whose citizens were arrayed against the government, and that the right of trial by jury was guaranteed to him by the Constitution of the United States...

The importance of the main question presented by this record cannot be overstated; for it involves the very framework of the government and the fundamental principles of American liberty.

During the late wicked Rebellion, the temper of the times did not allow that calmness in deliberation and discussion so necessary to a correct conclusion of a purely judicial question. Then, considerations of safety were mingled with the exercise of power; and feelings and interests prevailed which are happily terminated. Now that the public safety is assured, this question, as well as all others, can be discussed and decided without passion or the admixture of any element not required to form a legal judgment. We approach the investigation of this case, fully sensible of the magnitude of the inquiry and the necessity of full and cautious deliberation...

The controlling question in the case is this: Upon the facts stated in Milligan's petition, and the exhibits filed, had the military commission mentioned in it jurisdiction, legally, to try and sentence him? Milligan, not a resident of one of the rebellious states, or a prisoner of war, but a citizen of Indiana for twenty years past and never in the military or naval service, is, while at his home, arrested by the military power of the United States, imprisoned, and, on certain criminal charges preferred against him, tried, convicted, and sentenced to be hanged by a military commission, organized under the direction of the military commander of the military district of Indiana. Had this tribunal the legal power and authority to try and punish this man?

No graver question was ever considered by this court, nor one which more nearly concerns the rights of the whole people; for it is the birthright of every American citizen when charged with crime, to be tried and punished according to law. The power of punishment is, alone through the means which the laws have provided for that purpose, and if they are ineffectual, there is an immunity from punishment, no matter how great an offender the individual may be, or how much his crimes may have shocked the sense of justice of the country, or endangered its safety. By the protection of the law human rights are secured; withdraw that protection, and they are at the mercy of wicked rulers, or the clamor of an excited people. If there was law to justify this military trial, it is not our province to interfere; if there was not, it is our duty to declare the nullity of the whole proceedings. The decision of this question does not depend on argument or judicial precedents, numerous and highly illustrative as they are. These precedents inform us of the extent of the struggle to preserve liberty and to relieve those in civil life from military trials. The founders of our government were familiar with the history of that struggle; and secured in a written constitution every right which the people had wrested from power during a contest of ages. By that Constitution and the laws authorized by it this question must be determined. The provisions of that instrument on the administration of criminal justice are too plain and direct, to leave room for misconstruction or doubt of their true meaning. Those applicable to this case are found in that clause of the original Constitution which says, "That the trial of all crimes, except in case of impeachment, shall be by jury"; and in the fourth, fifth, and sixth articles of the amendments...

Have any of the rights guaranteed by the Constitution been violated in the case of Milligan? and if so, what are they?

Every trial involves the exercise of judicial power; and from what source did the military commission that tried him derive their authority? Certainly no part of the judicial power of the country was conferred on them; because the Constitution expressly vests it "in one supreme court and such inferior courts as the Congress may from time to time ordain and establish," and it is not pretended that the commission was a court ordained and established by Congress. They cannot justify on the mandate of the President; because he is controlled by law, and has his appropriate sphere of duty, which is to execute, not to make, the laws; and there is "no unwritten criminal code to which resort can be had as a source of jurisdiction."

But it is said that the jurisdiction is complete under the "laws and usages of war."

It can serve no useful purpose to inquire what those laws and usages are, whence they originated, where found, and on whom they operate; they can never be applied to citizens in states which have upheld the authority of the government, and where the courts are open and their process unobstructed. This court has judicial knowledge that in Indiana the Federal authority was always unopposed, and its courts always open to hear criminal accusations and redress grievances; and no usage of war could sanction a military trial there for any offence whatever of a citizen in civil life, in nowise connected with the military service. Congress could grant no such power; and to the honor of our national legislature be it said, it has never been provoked by the state of the country even to attempt its exercise. One of the plainest constitutional provisions was, therefore, infringed when Milligan was tried by a court not ordained and established by Congress, and not composed of judges appointed during good behavior...

It is claimed that martial law covers with its broad mantle the proceedings of this military commission. The proposition is this: that in a time of war the commander of an armed force (if in his opinion the exigencies of the country demand it, and of which he is to judge), has the power, within the lines of his military district, to suspend all civil rights and their remedies, and subject citizens as well as soldiers to the rule of his will; and in the exercise of his lawful authority cannot be restrained, except by his superior officer or the President of the United States.

If this position is sound to the extent claimed, then when war exists, foreign or domestic, and the country is subdivided into military departments for mere convenience, the commander of one of them can, if he chooses, within his limits, on the plea of necessity, with the approval of the Executive, substitute military force for and to the exclusion of the laws, and punish all persons, as he thinks right and proper, without fixed or certain rules.

The statement of this proposition shows its importance; for, if true, republican government is a failure, and there is an end of liberty regulated by law. Martial law, established on such a basis, destroys every guarantee of the Constitution, and effectually renders the "military independent of and superior to the civil power" — the attempt to do which by the King of Great Britain was deemed by our fathers such an offence, that they assigned it to the world as one of the causes which impelled them to declare their independence. Civil liberty and this kind of martial law cannot endure together; the antagonism is irreconcilable; and, in the conflict, one or the other must perish.

This nation, as experience has proved, cannot always remain at peace, and has no right to expect that it will always have wise and humane rulers, sincerely attached to the principles of the Constitution. Wicked men, ambitious of power, with hatred of liberty and contempt of law, may fill the place once occupied by Washington and Lincoln; and if this right is conceded, and the calamities of war again befall us, the dangers to human liberty are frightful to contemplate. If our fathers had failed to provide for just such a contingency, they would have been false to the trust reposed in them. They knew — the history of the world told them — the nation they were founding, be its existence short or long, would be involved in war; how often or how long continued, human foresight could not tell; and that unlimited power, wherever lodged at such a time, was especially hazardous to freemen. For this, and other equally weighty reasons, they secured the inheritance they had fought to maintain, by incorporating in a written constitution the safeguards which time had proved were essential to its preservation. Not one of these safeguards can the President, or Congress, or the Judiciary disturb, except the one concerning the writ of habeas corpus.

It is essential to the safety of every government that, in a great crisis, like the one we have just passed through, there should be a power somewhere of suspending the writ of habeas corpus. In every war, there are men of previously good character, wicked enough to counsel their fellow-citizens to resist the measures deemed necessary by a good government to sustain its just authority and overthrow its enemies; and their influence may lead to dangerous combinations. In the emergency of the times, an immediate public investigation according to law may not be possible; and yet, the peril to the country may be too imminent to suffer such persons to go at large. Unquestionably, there is then an exigency which demands that the government, if it should see fit in the exercise of a proper discretion to make arrests, should not be required to produce the persons arrested in answer to a writ of habeas corpus. The Constitution goes no further. It does not say after a writ of habeas corpus is denied a citizen, that he shall be tried otherwise than by the course of the common law; if it had intended this result, it was easy by the use of direct words to have accomplished it. The illustrious men who framed that instrument were guarding the foundations of civil liberty against the abuses of unlimited power; they were full of wisdom, and the lessons of history informed them that a trial by an established court, assisted by an impartial jury, was the only sure way of protecting the citizen against oppression and wrong. Knowing this, they limited the suspension to one great right, and left the rest to remain forever inviolable. But, it is insisted that the safety of the country in time of war demands that this broad claim for martial law shall be sustained. If this were true, it could be well said that a country, preserved at the sacrifice of all the cardinal principles of liberty, is not worth the cost of preservation. Happily, it is not so.

It will be borne in mind that this is not a question of the power to proclaim martial law, when war exists in a community and the courts and civil authorities are overthrown. Nor is it a question what rule a military commander, at the head of his army, can impose on states in rebellion to cripple their resources and quell the insurrection. The jurisdiction claimed is much more extensive. The necessities of the service, during the late Rebellion, required that the loyal states should be placed within the limits of certain military districts and commanders appointed in them; and, it is urged, that this, in a military sense, constituted them the theatre of military operations; and, as in this case, Indiana had been and was again threatened with invasion by the enemy, the occasion was furnished to establish martial law. The conclusion does not follow from the premises. If armies were collected in Indiana, they were to be employed in another locality, where the laws were obstructed and the national authority disputed. On her soil there was no hostile foot; if once invaded, that invasion was at an end, and with it all pretext for martial law. Martial law cannot arise from a threatened invasion. The necessity must be actual and present; the invasion real, such as effectually closes the courts and deposes the civil administration.

It is difficult to see how the safety of the country required martial law in Indiana. If any of her citizens were plotting treason, the power of arrest could secure them, until the government was prepared for their trial, when the courts were open and ready to try them. It was as easy to protect witnesses before a civil as a military tribunal; and as there could be no wish to convict, except on sufficient legal evidence, surely an ordained and established court was better able to judge of this than a military tribunal composed of gentlemen not trained to the profession of the law.

It follows, from what has been said on this subject, that there are occasions when martial rule can be properly applied. If, in foreign invasion or civil war, the courts are actually closed, and it is impossible to administer criminal justice according to law, then, on the theatre of active military operations, where war really prevails, there is a necessity to furnish a substitute for the civil authority, thus overthrown, to preserve the safety of the army and society; and as no power is left but the military, it is allowed to govern by martial rule until the laws can have their free course. As necessity creates the rule, so it limits its duration; for, if this government is continued after the courts are reinstated, it is a gross usurpation of power. Martial rule can never exist where the courts are open, and in the proper and unobstructed exercise of their jurisdiction. It is also confined to the locality of actual war.