Will was born and raised in Canaryville, Chicago.
Will has an argument with Manning when he says that her pregnancy is getting in the way of her decision making as she was choosing to use the last nitrogen tank they had to save the life of a newborn baby unlikely to survive rather than another patient who Will thought needed it more. He snatches the tank off her and uses it himself, saving his own patient. This angers Manning and she doesn't talk to him for a few days despite his constant apologies. She eventually forgives him.
Later on, Manning is about to deliver her baby and her mother-in-law comes to see her. Will clearly has feelings for her but her mother-in-law catches onto this quicker than she can and is upset. She tells him to stay from her as it has only been 6 months since her husband died. He obeys immediately and doesn't see her for the next few days. However, Helen finds out that Natalie is thinking about moving back home to Seattle. She then tries to get Will and Natalie together as she doesn't want Natalie to leave and go so far away, as she wants to be close to her grandson.
In Clarity, Natalie tells Will she is tired of being his punching bag. She asks him why is it always her. Will asks her if she really doesn't know and kisses her.
On 1x09, Dr. Halstead puts his career on the line for a woman who reminds him of his mother. It's in this episode that it is revealed his mother died of cancer. Had she had access to the experimental drugs available she could still be alive, according to him. So, when opportunity comes to provide that chance to a cancer patient Will takes it. However, in order to do so he disrespects the patient's wishes and resuscitates her. Not obeying a DNR is illegal. Jennifer Baker and her family decide to file a lawsuit against the Hospital and Will.
On 1x12, Will is about to commit career suicide. However, Connor stops him from making a big mistake. He tells him Will is a good doctor and the world needs good doctors. Will found out from Zoe that Jennifer was on the placebo. He was about to tell her.
In Us, Jennifer Baker is released from the Hospital as she is too ill to continue the trial. She passes away at her home, with her family. Dr. Halstead attends the funeral. Her husband, Sal Baker, thanks him for not giving up on his wife. Will is sorry she had to go through it all for a trial that ended up giving her the placebo and not the drug. However, he has to move on knowing he did the best he could. Jay, his brother, helps him see that.
In Lesson Learned, Will's first mentor is brought in with kidney failure and pneumonia. Everyone, including Sharon, is sure she won't make it, but Will is determined to keep going and trying. He's very emotional and wants to save Dr. Rowan and even lashes out the care home taker who comes to check in. Will replays the graduation speech Rowan gave over and over. At the end, he re-watches her say that you should always "treat the patient and not the disease" and this should be the one thing they take away from her. He decides to let her die in peace instead of giving her a bedridden life. Natalie comforts Will when he breaks down in the locker room, and Nina is upset to see them hugging each other.
Jay Halstead is Will's brother. The two are very close but Jay admitted some anger over Will going "off partying" in another country while their mother died of cancer, insisting that he couldn't be there because he was deployed but Will should've been there with her. His father is out of the picture. However, Jay is still very protective of Will. This was shown particularly when Will came to Chicago and was nearly immediately indirectly accused of murder. Jay refused to allow Voight and SVU question Will because he said Will was being blindsided. Will said he wanted to help as much as he could, but Jay didn't let him.
In Malignant, Will told Jay that he thinks Rhodes delayed in treating Herrmann. Jay tells 51, which annoys Will, who tells him he told him that confidentially, to which Jay replies that he never told him not to tell anyone and Will says he should've known. He says he won't tell him anything like this again, and Jay replies that he won't help his medical cases by passing on information from his cases either.
In Little Bit of Light, Jay tells Erin they need a break and tells her that he'll be staying with his brother while he sorts out his life, after Will comes to see Jay and tells him that his ex, Abby, is in town and looking for him and has tracked them both down. Jay is still married to her after he thought they were divorced, and Erin isn't happy. Jay says he'll stay with Will even after she tells him he doesn't need to leave.
In Generation Gap, Will and Jay helped their father out when he was experiencing heart problems. Jay stayed with him and phoned Will, who then came and took over. They both then waited with each other while their father was in surgery. Jay was comforting Will, who was more worried about the surgery going bad, which it didn't.
Will is close to Dr. Natalie Manning and admits to have a crush on her. He always looks out for her. However, she has a lot going on with her life at the moment and just isn't at a place where she can see herself with anyone after Jeff. They kissed in Clarity.
This begins to irritate Will's girlfriend, Nina, who indirectly makes it clear to Natalie that Will and her are together after she sees Natalie hug Will after a tough case involving his mentor.
In Deliver Us, Nina, Natalie and Will were caught up in a mess when Nina personally handed Natalie an autopsy highlighting her mistake. Will told Nat later on that it was because Nina felt jealous. Natalie told him she would be too, saying that they're more than co-workers. Will said they were 'close friends', but Natalie said she wasn't so sure about that, which upset her and she left. She then accepted Jay's invitation to the hockey game that Will turned down. However, later on when she asked Jay, Jay told Will to sort out his life because he saw Will was clearly uncomfortable with them hanging out.
Will has constant arguments/disagreements with Connor Rhodes over medical procedures. In The Beating Heart, Herrmann was stabbed and brought into Chicago Med. In Malignant, Rhodes and Severide argue over the best course of action for Herrmann after 51 starts questioning Rhodes' decision to perform emergency surgery and accusations over him delaying treatment. Things are made worse when 51 is insistent on getting answers and asks Jay to ask around for them. Jay asks Will whether he thinks Rhodes made the right call, to which Will replies that he personally thinks that Rhodes delayed. Jay passes this on to Severide, who calls out Rhodes in front of everyone. Rhodes is upset and angered and figures out that it was Will who told them. The two argue over this and Will is put in a tough spot.
However, their friendship has started to grow in recent episodes, evident in Connor helping Will out during his placebo trial with the patient Jennifer Baker.
In Generation Gap, Will was talking to Jay on the phone about their father's worsening heart condition. He tells Connor his father is stubborn so he won't come to the hospital so he'll have to check him out, so he's going by train. Connor tells him to use his car but he doesn't have one, so he offers his, but Will says he wants him to come too. They both go and Will stands back while Connor diagnoses Pat. It is also Connor who then performs Pat's open-heart surgery. Connor tells Will that he envies what he and his father have, because he and his dad don't even talk anymore.
Pat Halstead is Will and Jay's father. Not a lot was known about him except that he was out of the picture. However, in Generation Gap, Will was seen calling Jay, who was with their father, to make sure he was okay because of some heart problems. Will decided to give him a visit, and brought Connor with him. They checked him out but Pat was insistent that Will stay away from him. He refused to go to the hospital until Connor persuaded him to.
At the hospital, Mr Halstead wouldn't listen to anything Will had to say, telling him to stop trying to help him. Will was clearly very upset. Connor told Mr Halstead that they could either go for open heart surgery or a surgical clip that wouldn't involve surgery. Will said the surgery would be better but his father refused and he didn't say anything more and walked out, after he said that if he didn't agree with his choice, he should leave. Connor told him to try to talk to him at least, because surgery was better, which is when Will told him that his father considered him a "disappointment" because he believed that "real men" go straight to work and not college.
The clip doesn't hold up and Sharon and Connor take Pat to surgery, and Pat asks them not to tell Will because he will know he was right. Will and Jay wait for the update, and Will is more worried than Jay is. Inside, just before it starts, Pat starts talking to Connor. He tells him that Will was right. He says that he didn't want Will to go to college and wouldn't even pay for it when he did. He says he was wrong and that Will made something of himself despite what he kept telling him. Connor tells him he's probably proud, and Pat says he can't even begin to explain it.
The surgery goes fine and while Will tries to explain to his dad that he needs to take care of his heart from now on, and he interrupts him by holding him and telling him he was right. They both smile while Connor watches, as Connor had told Will that he doesn't even talk to his dad.
Will has been dating Nina, but things went badly after Nina saw him and Natalie hugging, after which she saw that he isn't interested in her. He doesn't share personal things with her and she began to notice this in Generation Gap.
In Deliver Us, Nina was again jealous to see Nat and Will together. Then Natalie missed something in a patient, which led to his death. She did the autopsy and gave him her the report personally, she made her upset when she found out. Will asked her why she personally delivered the report and she replied that Natalie should see her mistake, and later admitted she was jealous of the two. She said they didn't spend enough time together and he missed a hockey game with Jay to be with her that night, and Jay took Natalie instead.
Nina and Will broke up after Will told her he wasn't being fair to her in the relationship, in which he was referring to Natalie.