Who presides over Tom's trial in To Kill a Mockingbird?

Judge John Taylor presides over Tom Robinson’s trial.

Judge Taylor is a very good judge, but he does not look it.  In fact, he is described as “looking like a sleepy old shark” rather than an alert and conscientious judge.  Although he might chew on a cigar or clean his fingernails in court, or even appear asleep, he always pays attention.

He was a man learned in the law, and although he seemed to take his job casually, in reality he kept a firm grip on any proceedings that came before him. (ch 16)

Judge Taylor is aware of how important Tom Robinson’s trial is, which is why he chooses Atticus Finch to defend him.  He knows that Atticus will give him a vigorous defense, black or white.

During the trial, Judge Taylor keeps a close watch on the proceedings.  He enforces order, and keeps the witnesses—mainly Bob Ewell and his daughter—in line.  He makes sure that as much of an honest and fair trial as Tom can get, he gets.