Otto Anderson, a 63-year-old widower, lives in suburban Pittsburgh, Pennsylvania. After retiring from a steel company, he plans suicide, having lost his wife Sonya, a schoolteacher, six months previously.

During a suicide attempt by hanging, he is interrupted by his new neighbors: Marisol, Tommy, and their two daughters, Abby and Luna. Otto has flashbacks to his past; years previously he tried to enlist in the army but was rejected due to his hypertrophic cardiomyopathy. He meets Sonya on a train after returning a book she dropped.

Otto attempts suicide again, this time via carbon monoxide poisoning. He experiences a flashback to a dinner with Sonya, confessing to her that he is not enlisted in the army due to his heart condition and does not have a job, prompting Sonya to kiss him. Marisol disrupts Otto's suicide attempt, asking him to take her and her kids to the hospital after Tommy fell and broke his leg using a ladder Otto had lent to him. Otto reluctantly agrees.

Otto has a flashback to his graduation when he asked Sonya to marry him. During a suicide attempt by train, an old man faints and falls on the railroad tracks. Otto saves the man and the incident goes viral. Otto takes Marisol for a driving lesson and they visit Sonya's favorite bakery, which the couple formerly frequented every weekend. There, he tells her about his friendship with a man named Reuben, the two having worked together to establish rules and order, with Otto as chairman of the neighborhood association board. The two grew apart after Reuben's preference for Fords and Toyotas over Otto's Chevrolets and the "coup" of replacing Otto as chairman. Reuben, who had a stroke, now uses a wheelchair and is cared for by his wife Anita and neighbor Jimmy.

A local transgender teen, Malcolm, recognizes Otto as Sonya's husband while delivering newspapers and circulars in the neighborhood. Malcolm cuts through Otto's disgruntlement at receipt of the newspapers and recounts that Sonya was his teacher, and one of the few people who accepted him as he was. A friendship forms between the pair and Otto fixes Malcolm's bicycle. After dodging a social media journalist named Shari Kenzie who is attempting to interview Otto in relation to the earlier viral video, he gets angry at both Marisol and a Dye & Merika real estate agent, not wanting to come to terms with Sonya's death. He attempts to commit suicide by shotgun, but is interrupted by Malcolm, who asks to spend the night after his father kicked him out.

Otto learns that Dye & Merika is planning to force Reuben into a nursing home and take their house, after illegally finding out that Anita was diagnosed with Parkinson's disease. Otto agrees to help Anita and Reuben. Marisol refuses to assist Otto until he tells her that he and Sonya went to Niagara Falls to celebrate Sonya's pregnancy. On the bus back home, they were involved in a crash, and Sonya became paralyzed and had a miscarriage. The neighborhood was not accessible to Sonya and Otto was voted out of the chairmanship after a heated confrontation with a Dye & Merika representative. Otto wanted to put all of the real estate companies out of business but decided against it to care for Sonya. With the help of the neighborhood and Shari Kenzie, Reuben and Anita are able to keep their home.

Otto collapses and is taken to the hospital, where he lists Marisol as his next of kin. After being told by a cardiologist that Otto's heart is too big, she laughs, before going into labor and gives birth to a son.

One day, Tommy notices that Otto did not shovel the snow on his walkway. Marisol and Tommy enter Otto's house to find him dead, having succumbed to his enlarged heart. A funeral is held, attended by his neighbors. In a letter to Marisol, Otto says that his lawyer will give her his bank accounts, providing them with enough money to take care of her family, along with his new car and house.

Ove Lindahl, a 59-year-old widower, lives in a townhouse neighborhood where he was the chairman of the neighborhood association until Rune, his former friend, replaced him. Rune is now paralysed after having a stroke and being cared for by his wife, Anita. Ove is depressed after his wife, Sonja, a schoolteacher, died from cancer six months previously. Having worked at the same company for 43 years, he is pushed into retiring. His attempts to hang himself are repeatedly interrupted by Iranian immigrant Parvaneh, her Swedish husband Patrick, and their two children, who are moving into the house across the street.

During another suicide attempt, Ove flashes back to his childhood. His mother died when he was a child, leaving him alone with his quiet father, a mechanic at the train company. His father shared his knowledge of engines with Ove, who had a part-time job at the train yard. Having done particularly well at his exams, he reports his results to his father, who is so anxious to spread the news that he fails to take proper care and is hit by a train and killed.

In the present, during another attempt to kill himself, this time by carbon monoxide poisoning, Ove is sitting in his running car and again recollects the past when he began working at the train company. Two men from the local council, whom Ove dubs "The Whiteshirts," arrive at young Ove's home and declare it should be demolished. Ove instead fixes the house. His neighbor's home catches fire one night, and Ove saves two people, but sparks from the fire cause his own home to burn, and The Whiteshirts prevent the fire from being tackled because they plan to demolish it in any case.

With nowhere to go, Ove sleeps on a train at work; he wakes to find a young woman, Sonja, sitting across from him. He is smitten with her and returns to the same early train each morning. After three weeks, he finds her again, and they begin dating. She encourages him to return to school, and he earns a degree in engineering.

Ove's attempt to kill himself is interrupted by Parvaneh banging on the garage door, wanting a lift to the hospital because her husband has had an accident. Ove takes care of Parvaneh and Patrick's two daughters, Sepideh and Nasanin, and is made to sit outside after he causes a scene. Later, Ove goes to the train station, planning to jump in front of a train. However, when a man on the platform faints and falls onto the tracks, Ove jumps down and rescues him.

Parvaneh asks Ove to teach her how to drive, and he eventually agrees. He also takes in a stray cat which he had previously found an annoyance. He tells Parvaneh about his past friendship with Rune and how they worked together to establish rules and order, with Ove as chairman of the neighborhood association board and Rune as the deputy chair. They grew apart over the years because Rune preferred Volvo cars and Ove Saabs until Rune organized a "coup" and replaced Ove as chairman. He also begins to bond with his new cat. He repairs a bike he confiscated from a neighborhood teen, Adrian, and returns it to Adrian, who works at a kebab shop with another youth called Mirsad. Ove notices Mirsad's eye makeup and wonders if he is "one of those gays" but does not shun him.

Despite his improved relations with his neighbors, Ove has an altercation with two "Whiteshirts" attempting to force Rune into a nursing home. Ove attempts suicide using a shotgun but is interrupted by Adrian and Mirsad ringing his doorbell. Adrian says Mirsad had been kicked out of his house after coming out to his family and needs a place to stay. Ove reluctantly invites Mirsad in. Later, Ove tells Parvaneh how, when pregnant, Sonja wanted to go on vacation before the baby arrived. She and Ove traveled on a tour bus to Spain, but on the journey home, the bus crashed. In the crash, Sonja lost the baby and her other injuries forced her to become reliant on a wheelchair, which made her unable to take a job as a teacher. When the local authorities ignored Ove's pleas to build a wheelchair ramp, he goes to the school at night and builds one.

Ove collapses and is taken to the hospital, where he lists Parvaneh as his next of kin. Parvaneh is told that her "father" has an enlarged heart but will survive. Laughing, she tells Ove he is terrible at dying before going into labor and delivering a boy. Ove gives gifts to Parvaneh's daughters, who refer to him as grandpa.

Several months later, Parvaneh wakes to a winter storm and notices that the ever-punctual Ove has not cleared his pathway. She and Patrick run to Ove's house to find he has died. Ove, having found peace, has left strict instructions for his funeral; the service is packed with neighbors. The film ends with Ove waking on the train where he first met Sonja to find her waiting for him in the afterlife.