The story is rich in situational irony.
Situational irony can be broadly defined as situations where the outcomes are incongruous to what is expected, or situations which involve contrasts and/or clear contradictions.
The first example of this is when, on his arrival, Mrs Lucynell Carter deems Tom T. Shiftlet as a tramp and "no one to be afraid of". Mr Shiftlet proves to be just the opposite later in the story when he steals their car and abandons the younger Lucynell in a diner. Tom's statement that:
"I'd give a fortune to live where I could see me a sun do that every evening".
is also deeply ironic, for he later deserts his wife and travels to Mobile in the stolen car.
A further example of situational irony would be the fact that Tom has only one fully usable arm. The expectation would be that this would hamper him in the performance of his tasks, but he expertly and efficiently completes a number of tasks around the plantation and the house, including repairing the Carter's broken car.
Tom also declares that he is looking for an honest woman, but after marrying Lucynell junior, who is wholly innocent and pure, he dumps her at a diner. He had the opportunity to start a new life with an untainted woman, but abandons that ideal.
It is also ironic that Tom later alludes to his purity and honesty by comparing himself to monks, when he is told that he should sleep in the car. He mentions that the monks of old slept in their coffins. However, he later steals from his hosts.
A great many of the examples of irony are contained in what the characters say and what they actually do. There is a distinct contrast between the two. Mr Shiftler tells Mrs Carter that although he is not a "whole" man, he has "moral intelligence", a statement that is devoid of any truth if one considers his actions later. Mrs Carter, on the other hand, states that she would never give up her daughter "for a casket of jewels" but literally sells her off to Tom Shiftler for seventeen dollars fifty.
The greatest irony lies in the act that Tom Shiftler is presented as a redemptive figure when he stretches out his arms to represent a crooked cross - alluding to sacrifice. He is, however, anything but. He abuses and exploits the kindness extended to him when he eventually makes off with some of the Carter's money and their car. He had been given the opportunity to find stability in his aimless and meaningless life, yet he chose to discard it and continue his shiftless, mundane existence.
The form of irony used in this story is situational irony. "Situational Irony occurs in literature and in drama when persons and events come together in improbable situations, creating a tension between expected and real results."
Shiftlet meeting Lucynell and her mother, as well as Mrs. Crater marrying her daughter off to this odd drifter, set up a tension for the reader. We don't trust Mr. Shiftlet, and the reader is uncomfortable with Mrs. Crater's actions. The end of the story is ironic because Mr. Shiftlet has found salvation from his meaningless life in his relationship with Lucynell.
Mr. Shiftlet, who finds himself in the situation with Lucynell and her mother, which actually could have provided him with a decent sort of life,instead of accepting this chance at a meaningful life, he abandons his salvation, Lucynell in a diner.
The irony is that other characters recognize Lucynell as an "Angel of Gawd" but Shiftlet does not see it. He abandons Lucynell, and a life saved, to resume his wandering and aimless life.