In Harper Lee's classic novel To Kill a Mockingbird, Judge Taylor appoints Atticus Finch to defend Tom Robinson in front of what will be a racist jury and audience. Judge Taylor recognizes Atticus as a moral man who champions racial equality and will valiantly defend an innocent client like Tom Robinson regardless of his race. Typically, court-appointed defenses are given to inexperienced lawyers like Maxwell Green. However, Judge Taylor supports Tom Robinson and chooses Atticus for the job because he knows Atticus will challenge Maycomb's prejudiced court system.

Even though Atticus is appointed to Tom Robinson's case, he makes the courageous decision to vigorously defend him rather than succumb to racial prejudice and allow the prosecutor to have his way. During a conversation about the upcoming trial, Jack asks Atticus if he will "Let this cup pass" and Atticus responds by saying,

"Right. But do you think I could face my children otherwise? You know what’s going to happen as well as I do, Jack, and I hope and pray I can get Jem and Scout through it without bitterness, and most of all, without catching Maycomb’s usual disease."

Although Atticus seems to have considered not taking the case, he feels he has no choice but to set a good example for his children by championing racial equality in order to prevent Jem and Scout from catching "Maycomb's usual disease." He does not want them developing into cynical, racist individuals like the majority of their neighbors.

As a morally upright man, Atticus knows that he must defend Tom Robinson in order to act as a positive role model for his children and teach them valuable attributes. Atticus hopes to show Jem and Scout the importance of courage, integrity, and obeying one's conscience. He also wants to demonstrate the importance of protecting innocent, defenseless individuals. When Scout asks Atticus why he is defending Tom Robinson, Atticus says,

"The main one is, if I didn’t I couldn’t hold up my head in town, I couldn’t represent this county in the legislature, I couldn’t even tell you or Jem not to do something again."

Atticus's comments once again reveal that he is motivated to defend Tom Robinson in order to live up to his own moral standards and solidify his strong beliefs. His conscience influences him to take a stand against racial prejudice and prove Tom's innocence.

Atticus Finch defends Tom Robinson in To Kill a Mockingbird by Harper Lee. Living in Maycomb, Alabama, in the 1930s means that Atticus will have to defend not only Tom but his beliefs and his family as well. Prejudice in Maycomb was just as strong as it was in 1864 during the Civil War.  Many of Maycomb’s citizens believe that black people are sub-human.

The trial of Tom Robinson gives Atticus opportunities to teach the children about prejudice and its impact on people both black and white.  Jem, as he matures, begins to understand the ugliness of bigotry as seen inside and outside the courtroom during the trial. 

Why did Atticus defend Tom Robinson when he knew that he could not win the case? This unique man explains it to his children:

"If you shouldn't be defendin' him, then why are you doin' it?"

"For a number of reasons," said Atticus. "The main one is, if I didn't I couldn't hold up my head in town, I couldn't represent this county in the legislature, I couldn't even tell you or Jem not to do something again…Scout, simply by the nature of the work, every lawyer gets at least one case in his lifetime that affects him personally. This one's mine, I guess."

Integrity and character are two of the traits that Atticus tries to instill in his children.  He must demonstrate these qualities himself.  Atticus commits to treating everyone the same.  He does not believe in violence which often occurs in the story.

As a lawyer, Atticus promises to defend anyone that needs his help.  The judge assigned him to the case, but Atticus would have taken the case anyway. 

The case cannot be won at this time in the south.  Neither women nor black people serve on the juries.  Everywhere a person turns there is bias----against women, blacks, people like the Cunningham and the Ewells.

To definitively answer the question, Atticus defends Tom Robinson because it is the right thing to do.  There will no change in prejudice until everyone receives the same treatment in the court system which Atticus states “is the great leveler of all people.” All people deserve a fair trial and a fair judgment by their peers.

Tom Robinson did get the trial in which everything that needed to be said was stated. One small step was taken: the Cunningham man did not want to vote guilty. The jury stayed  out longer than any other black person's jury.   Atticus knew that even one juror might lead to the next trial where five jurors might vote not guilty.

As Mr. Dolphus Raymond tells Scout in front of the court house:  “…you don’t your pa’s not a run-of-the mill man…”

Harper Lee’s To Kill a Mockingbird is set in Depression era rural Alabama. For the white and African American residents, segregation and racism are accepted parts of life. Even so, Atticus Finch, in his role as defense attorney, strives that every individual charged with a crime receive a fair trial.

When Atticus is appointed to the position of Tom Robinson’s attorney, he accepts. For him, there is much on the line. He is a respected attorney defending an African American man accused of beating and raping a white woman. In the eyes of many of Maycomb’s residents, Atticus taking the case is nothing less than betraying the white race he represents. Yet for Atticus, his view of equal justice extends further than the courtroom. When he hears rumors that some residents plan to kidnap Tom from his jail cell and lynch him, Atticus decides to guard the cell knowing that the mob might harm or kill him in its attempt to get to Tom.