Edwin Poole is introduced as one of three founding and name members of the show's depicted law firm, Crane, Poole & Schmidt, along with two of the more central characters in Boston Legal, Denny Crane and Shirley Schmidt. He is referenced to have been a spectacular trial lawyer in the past, however, during the first episode of the series, Edwin Poole suffers from a mental breakdown and is admitted into a psychiatric hospital.
Later in the first season, he temporarily leaves the hospital and agrees to try a criminal case as the defending attorney, a lifelong ambition of his. He receives assistance from Crane, Poole & Schmidt attorney Lori Colson, who was told both by Paul Lewiston and the judge to supervise his actions. When his side didn't win after he forgot to prepare a closing argument, he recognized that he was no longer acting in his full capacity and agreed to return to the psychiatric facility.
Near the end of the second season, Edwin makes another appearance, this time after being released from the hospital after becoming well. The first day back at the office he decides to sue a disease (diabetes) and then a candy company for causing his overweight client's diabetes. After jumping into the lawsuit, not preparing any research, and publicly defaming the company in a press conference, Shirley suggests that he is not quite well yet and should check himself back into the hospital for further treatment.