I would agree that the separation of powers which provides for the system of checks and balance is one important ingredient in ensureing that justice is achieved. To add to the above post, we are to be judged by a jury of our peers, so we could also so say that involvement of individuals in the process also ensures justice
In order to answer this question, one has to look at the meaning of “justice”. Justice can be defined as the administration of law. In order to establish justice, the country needs a legal system that makes decisions fairly. How this is done is by creating a federal judiciary. Before the Constitution, under the Articles of Confederation, there was no judicial system which created a great deal of problems for the United States. Article Three of the Constitution created a federal judiciary system to establish justice in the U.S. Article Three, Section One states “The judicial power of the United States shall be vested in one Supreme Court, and in such inferior courts as the Congress may from time to time ordain and establish.” To further establish justice, Article Three Section Two states “The trial of all crimes, except in cases of impeachment, shall be by jury; and such trial shall be held in the state where the said crimes shall have been committed; but when not committed within any state, the trial shall be at such place or places as the Congress may by law have directed.” The Supreme Court under the Constitution is an appellate court, which means that those who feel that justice was not done in their particular case have the power to appeal an unfair decision, further establishing justice in the U.S. Finally, federal justices are given lifetime appoints, which will keep politics out of their decisions, further ensuring justice within the U.S.
Building on the answer above, the Constitution not only provides for the creation of a separate judicial branch and a Bill of Rights to protect citizens from government abuses of power, but it specifies that the Judiciary be independent, meaning that once they are appointed to federal court positions, they are in office for life, or until they resign or are impeached.
This prevents government from exercising undue influence over court rulings, therefore ensuring those rulings be as just as possible in a system created and administered by humans. The Bill of Rights, then, gives individuals permanent legal grounds to challenge government actions and court convictions.
One way to answer this would be to say that the Bill of Rights ensures that justice is established. You could argue that the inclusion of the Bill of Rights ensures that the government cannot take away our rights -- this is one definition of justice.
However, it is more appropriate to say that the system of separation of powers and checks and balances is meant to ensure that justice is achieved. The government can violate the Bill of Rights (and other parts of the Constitution) and it has done so in the past by allowing things like segregation and the Alien and Sedition Acts.
Because the government can defy the Constitution, the only thing that can be done is to make it as hard as possible for this to happen. That is what the Constitution does with the separation of powers and checks and balances. These two aspects of the Constitution make it harder (but not impossible) for the government to abridge our rights.
So the best answer for this is to say that the system of separation of powers and checks and balances is our best hope for establishing justice.