Middle-aged and somewhat naïve, Chance has spent his entire life in a wealthy old man's townhouse in Washington, D.C., where he is cared for by the kind African-American maid, Louise. His life revolves around tending to the garden and consuming information exclusively from television. When the old man passes away, Chance is unceremoniously evicted by the estate's lawyers, forcing him to navigate a world he has never experienced.
As he wanders outside for the first time, he encounters danger when a young African-American man brandishes a knife. In a comically futile attempt to escape, Chance tries to use a TV remote control on him. Strolling past a TV shop, Chance is captivated by his own image on a live video feed. Distracted, he backs up into the street and is hit by a limousine driven for Eve Rand, the glamorous and much younger wife of elderly tycoon Ben Rand. When she inquires about his name, she mistakenly interprets "Chance, the gardener" as "Chauncey Gardiner".
Eve takes Chauncey to their opulent estate, where Dr. Allenby, a physician caring for Ben, assesses him and invites him to stay. Chauncey’s old-fashioned manners and eccentric style—complete with outdated but expensive attire from his late employer’s attic—allow him to blend into high society. When Ben meets him, he mistakenly perceives "Chauncey" as a sophisticated businessman who has fallen on hard times, admiring him for his candidness and apparent wisdom.
Ben, a close advisor to the President of the United States, introduces Chauncey to the President. During a conversation about economic growth, Chauncey’s innocent remarks about gardening—using the phrase "stimulate growth" as a metaphor for changing seasons—are misinterpreted as political strategy. Much to his surprise, Chauncey then becomes a media sensation, gaining national acclaim and attending significant events while developing a unique rapport with the Soviet ambassador. Despite his rising fame, Louise observes, in dismay, that Chance’s success stems from the privilege of his race, proclaiming that he has "rice pudding between the ears.”
While Chance enjoys the pinnacle of Washington’s social scene, his enigmatic background remains a mystery to the Secret Service and various foreign agencies. However, Dr. Allenby grows wary of Chance, suspecting that the truth behind his identity is far less glamorous. Although tempted to reveal the truth to Ben, Allenby remains silent, recognizing the joy Chance brings during the elderly man's final days.
As Ben encourages Eve to pursue a relationship with Chauncey, she becomes increasingly attracted to him. Despite being oblivious to sexual advances, Chance mimics a kissing scene he sees on the television, but loses interest as he becomes distracted by another program. This leads to an unexpected moment of intimacy, yet Chance remains absorbed in his television multitasking.
Mourning Ben’s passing, Chance is genuinely heartbroken, reflecting on his feelings for Eve, admitting his love while maintaining his identity as merely a gardener. After this revelation, the President delivers a speech at Ben’s funeral, where the pallbearers quietly contemplate potential successors, agreeing that "Chauncey" would make a suitable candidate. Unfazed, Chance wanders through the estate’s winter landscape, tenderly straightening a sapling knocked over by a falling branch. To the astonishment of onlookers, he walks across a frozen lake without sinking, and with a simple dip of his umbrella into the water, he radiates an aura of enigmatic tranquility, as the President echoes Ben’s words: > "Life is a state of mind."
