There are several ironic developments in Hemingway's "The Snows of Kilimanjaro." Perhaps the most obvious is the situational irony involving Henry's purpose for going on the safari--to become inspired, more alive as a writer. The mountain represents for Harry inspiration, purity, renewal as an artist. Instead, he meets his death through gangrene--a rotten leg--an ignoble end to a lofty goal.
Also ironic is his marriage, which should perpetuate life through procreation, but instead stifles Henry's life and creativity. He feels as if he has sold out by marrying a rich woman. Instead of bringing Harry love and fulfillment, his marriage has resulted in a stifled career and a sense of waste and emptiness. In many ways, Harry is spiritually dead before he physically dies. Harry wanted to write poetry and stories; now because of his gangrene, he has become the story he might have written. Just as Harry fails to climb the mountain on the safari, he has failed as a writer.
Another source of irony might be in the interpretation of the animal symbolism, a topic explored by Jerianne Wright, in a short but interesting essay whose link I have posted below. Harry would have preferred to be more like the leopard who ascends the mountain independently, but his life has been more like the hyenas who settle for what can be scavenged.