Harold Mitchell is first seen as one of the four poker players in the third scene. The players speak coarsely, enjoying primitive, direct humor, mixing it with the cards, chips, and whiskey — that is, all except Mitch. He seems to be somewhat different. He is first distinguished from the other three when he is teased about his concern for his mother. He excuses this soft-heartedness by explaining that she is ill and unable to sleep until he comes in at night. In disdain, the hot-tempered Stanley tells him to go home. A few lines later, a second aspect of Mitch is revealed as he meets Blanche DuBois. His awkward courtesy and embarrassment show a consciousness of manners seldom seen in that raffish section of New Orleans. Blanche is quick to notice the hint of sensitivity in him that makes him seem superior to the others. Although he carries a silver cigarette case engraved with a quote from a sonnet, his words describing the romance and sorrow that inspired it seem trite and inadequate. At this point, Blanche provides the imagination and sympathy, while Mitch answers with his characteristically sincere commonplaces. His sensitivity appears rather clumsy in comparison, but he does half-apologize, saying that Stanley and his friends must strike Blanche as a pretty rough bunch. Mitch's awkward imitation of the romantic gestures of Blanche is shown in the stage direction of this scene. He is a "dancing bear" following the steps of her waltz. But this first appearance does characterize Mitch as the most sensitive member of the Kowalski world.
Mitch's limitations become more and more apparent as the play progresses, especially as Blanche believes she has found in him the kindness she so desperately needs. He is the representative of the decent gentleman who could save Blanche from the past from which she is trying to flee. However, we must remember that it is only in the rough society of men like Stanley that Mitch can be considered a valuable discovery. Blanche would be more aware of the differences in education and temperament if she were not in such immediate danger of breaking down emotionally. In the sixth scene, as they return from an evening at the amusement park, one sees the disparity in their intellects. Mitch only dimly feels that Blanche is laughing at him as he says he has never met anyone like her. She has succeeded in presenting a convincing image of innocence and sincerity; he accepts the appearance in tolerant good nature. The respect he affords her in not attempting to make love to her again separates him from Stanley. There is a contrast between his proud discussion of his physique and his mild request that Blanche can "just give him a slap" when he steps out of bounds. One is impressed by the wide gap of perception between him and Blanche. She is playing a role with demureness and delicate deceit while Mitch talks of himself in the bragging fashion of a young boy.
As soon as Mitch mentions his mother, Blanche draws him to the subject of love, seeing in him a warmth and "capacity for devotion." She tells him at last the story of her early marriage, in which lies the source of her torment. Mitch again responds awkwardly but is deeply moved. His sympathy and momentary understanding are sincere. At that point, he is at his highest in the play, although brought there by the influence of Blanche. It is in the denouement that he is again won over by the power of the world of Stanley, but for a brief moment Mitch had the possibility of saving the fragile Blanche and of being redeemed by her. The very characteristics that make him ordinary would have been indispensable to her — his honesty, stability, loyalty, and love. It is consistent with his lack of imagination that he should leave Blanche when confronted with her past. He could not see through her acting during the summer, for she herself had come to believe in her role. Her world where truth and fiction are blended was incomprehensible to him. Mitch failed to understand that Blanche could sincerely tell him, "Never inside, I didn't lie in my heart." His world crumbled, and he was unable to perceive the actual depth of Blanche's feelings.
In the last scene Mitch is once again playing poker, moody and ill-tempered. He bursts out at Stanley angrily, betraying his uneasiness. He is unable to concentrate on the game when he hears Blanche's voice, although several weeks have passed since their previous meeting. By staring down at his hands on the table, he is able to maintain the control he loses a few minutes later. Alone in his sympathy for Blanche, especially as he understands her aversion to this destructive environment, he lashes out wildly at Stanley. He seems to blame Stanley for interfering with a relationship that should have been left alone, but then he collapses in ineffectual sobs. Mitch fails by realizing too late the vulnerable beauty of Blanche and thus, he is left as lonely and alone as Blanche.