Much can be said about the book of Esther, but this post will be about the irony contained in it, overt and subtle.
The story told in Esther results in a memorial holiday called the Feast of Purim which is celebrated by Jews to this day. It was called Purim because Haman cast the Pur (like casting dice) to determine the day that all the Jews would be killed. This is overt irony, as the name for the holiday of the Jew’s being saved from death is based on the method used to determine their date of execution!
Two other obvious incidents of irony involve Haman. Haman hated Mordecai, and was also an arrogant man. When the King asked him how he should bring honor to someone, Haman assumed the King wanted to honor him, and told him the individual should be put in royal robes and paraded throughout the city. The individual to be honored turned out to be none other than Mordecai, whom Haman hated! It was Haman’s job to carry out this honorary treatment of Mordecai. Prior to this, Haman had built gallows for the purpose of one day hanging Mordecai on them. However, when Queen Esther revealed Haman’s subversive plot to kill the Jews, the King ordered Haman hung on his very own gallows.
An example of less obvious irony would be that in chapter one a decree is made by the King that Queen Vashti be deposed, and all wives in the kingdom are to obey their husbands (in reaction to the fact that Queen Vashti refused to come when the King called her). While in chapter nine, we see that the King gives commands based on instruction from Queen Esther (9:12-15). Furthermore in 9:32 it states that the decree of Esther confirmed the details of Purim. At the beginning of the book, wives must obey, and at the end of the book, Esther is being obeyed.
A final and fifth example of irony is related to this as well. When Queen Vashti refuses the King’s command, he issues a decree to help him retain authority over women in the kingdom. However, his new wife Queen Esther will disobey him by coming to him without being called, which was against the law (Esther 4:11, 5:1-2).