New York City bouncer Frank "Tony Lip" Vallelonga (Viggo Mortensen) finds himself in search of a new job after the nightclub he works at is temporarily closed for renovations. Although he harbors racial prejudices, his wife Dolores (Linda Cardellini) does not share his views. In a fortunate twist, Tony receives an invitation for an interview with Dr. Donald Shirley (Mahershala Ali), a talented African American pianist in need of a driver for an extensive eight-week concert tour through the Deep South. Don decides to hire Tony based on his strong references, and they set off with the intention of returning to New York by Christmas Eve.
During their journey, Don provides Tony with the Green Book, a crucial guide for African American travelers to locate motels, restaurants, and gas stations that cater to their community. Their tour starts in the Midwest, gradually moving southward. Initially, Tony and Don struggle to get along. Tony feels uneasy with Don's requests for refined behavior, while Don finds Tony's habits—such as urinating in public and his gambling and cursing—repulsive.
As the tour unfolds, Tony begins to appreciate Don's extraordinary piano talent and becomes increasingly appalled by the blatant discrimination Don faces, both from their hosts and the general public when he is not performing. After a group of white men threatens Don's safety in a bar, Tony springs into action and instructs Don to refrain from going anywhere without him for the rest of the tour. Throughout this eye-opening experience, Don assists Tony in composing heartfelt letters to his wife, evoking a deep emotional response from her.
Tony urges Don to reconnect with his estranged brother, yet Don hesitates, feeling the weight of isolation brought on by his professional success. In a troubling encounter at a YMCA pool, Don is found in a compromising situation with a white man, and Tony steps in to bribe the officers and prevent Don's arrest. The situation escalates when both men are arrested after a late-night stop in a sundown town, leading to a heated confrontation that ends with Tony punching an officer after being insulted. In their cell, Don asks to contact his "lawyer," managing instead to reach Attorney General Robert F. Kennedy, who intervenes to secure their release. While Tony is in awe of this encounter, Don feels humiliated, which triggers an intense argument between them.
Don expresses his turmoil, revealing that his wealth alienates him from his own race, while his race confines him from being accepted by whites, leaving him with an overwhelming sense of loneliness.
On the final night of their tour in Birmingham, Alabama, Don faces racial discrimination when he is denied entry into the whites-only dining room of their hotel. In an act of defiance, Tony confronts the owner, while Don resolutely refuses to perform unless he is granted the same dignity as his audience. They opt to play at a predominantly Black blues club, where Don's music electrifies the crowd.
As they make their way back north through a snowstorm, determined to arrive home for Christmas Eve, a fatigued Tony relinquishes driving to Don. They successfully return in time for Tony's family dinner, where he extends an invitation to Don. Ultimately, while Don initially heads back to his apartment, he makes the sincere choice to join Tony's family gathering, where he is greeted with warmth and acceptance after a moment of surprise.
