Steinbeck is a young man with an average height and build, with short blonde hair and blue eyes. He wears a flat cap on top of his head, a white shirt with his sleeves pulled up a bit, a blue overall with a black belt, and dark boots. He carries with himself a raw potato and a navaja, a tool he uses in order to activate his ability.
Steinbeck appears to be a relaxed and easygoing man, casually commenting about the countryside and talking with his partner, Howard Phillips Lovecraft, without minding being heard. His ability grants him great confidence in himself, enough to spend time talking to his enemies, which can also be his downfall.
He claims to hate chores, trying to save himself some trouble while doing them, which demonstrates that he is a cunning person. Nevertheless, he is in no way a lazy person, as he is capable enough to carry the missions given to him. Although he may be polite and kind, he shows no regard for his enemies, claiming to not care about what he has to do to them. At the same time, he is not an entirely bad person, driven by motivation of doing his job for his family.
Steinbeck's ability, The Grapes of Wrath (怒りの葡萄, Ikari no Budō?) allows Steinbeck to grow grapevines from any part of his body. By grafting the vines attached to his body to other plants, the flora in the entire vicinity becomes an extension of his body.
His own branches, as well as the others from the flora, can be used as a means to capture and hold a person or object with tremendous strength, as well as shield him from attacks.
He can even combine his ability with Q's, due to the fact that Q's ability is cursing people who hurt them. Fitzgerald's emergency plan involved both of their abilities: Steinbeck using his Grapes of Wrath to connect the plants directly into Q's body, affecting their sense of touch. Thus, when a person harms a plant in any way, it hurts Q, causing the person to get cursed.
Prior to joining the Guild, Steinbeck was a farmer in North America. It is implied that his large family was poor during such time.
The Guild Arc Steinbeck first appears where he's shown on the ground after crashing his truck, then complaining about the country's narrow roads. After getting up, he talks with Lovecraft about a package about to be delivered. Sometime later, he shows up with his partner in the middle of the conflict between the Armed Detective Agency and the Port Mafia, warning them about the arrival of the package (which is nothing more than ability users from the Guild). After wiping out both factions, he retires with the rest of his partners.
John shows up later in the countryside together with Lovecraft after accepting the Mafia's proposal to capture the clerks from the Armed Detective Agency as bait, even though they knew it was obviously a trap. In the next chapter, they are seen waiting to ambush the clerks, where he then activates his ability in order to capture them. The clerks attempt to escape by car via another route, but due to the propagation of his ability, the car is caught easily. There, he has a small conversation with Naomi, revealing information about his ability and himself. But thanks to this, he loses precious time and gets surprised by Kunikida and Tanizaki, whom he then engages in combat. He loses the battle and is stripped of his vines.
But thanks to the time bought by Lovecraft, he is able to stand once again and make use of his ability, catching the clerks once more. He then has a small talk with Tanizaki. During the conversation, he notices a single truck drifting off its lane thanks to Light Snow. Having no time to react, the vehicle crashes into him and Lovecraft.
It's discovered that they survived, but just as they are about to resume the pursuit, they get arrested by the police. 
Steinbeck, together with Lovecraft, appears again later on where they both ambush Dazai who came to rescue Q. However, Chūya makes an unexpected appearance, resulting in their defeat and Q's rescue. 
After the Guild's fall, Steinbeck is shown to have lost most of his foot during the battle during the previous fight with Chūya Nakahara and Dazai Osamu. Steinbeck says that he will stay, protecting what's left of the Guild as their Leader had gone missing. 
During Fitzgerald's comeback, while he was planning to rebuild the Guild, an infuriated Steinbeck observes Fitzgerald and Louisa May. He says that he will crush Fitzgerald's ambitions, but still wanting to befriend his former leader. 
Though he is one of the Guild's members, he hates Fitzgerald due to his endless ambition and arrogance.
- He made an appearance in the mobile game "Kimito Lead Puzzle 18" as a stage boss and a limited-time character.
- The name of his siblings is based on the actual characters from The Grapes of Wrath.
- He seems to like eating potatoes.
- John is actually good at making impressions.
- Much like Tanizaki, he cherishes his own little sister quite a lot, constantly spoiling her.
- Steinbeck is formerly a farmer before joining the Guild similar to Tom Joad, the main character from the real-life John Steinbeck's The Grapes of Wrath.