In 1963 Wyoming, two young men, Ennis Del Mar and Jack Twist, are hired for the summer to tend sheep on Brokeback Mountain. Ennis is reserved and quiet, with a fiancée at home, while Jack is more outgoing and dreams of being a rodeo cowboy. Isolated from the world on the mountain, the men form a deep bond born out of loneliness and a shared sense of companionship. One cold night, this bond morphs into a sexual relationship, a profound connection that surprises them both. Despite the intensity of their feelings, they part ways at the end of the summer, Ennis returning to marry his fiancée, Alma, and Jack continuing his pursuit of the rodeo circuit, aiming to forget what transpired on the mountain.

Years pass, and both men lead separate lives, with their experiences on Brokeback Mountain lingering as a silent, hidden part of their past. Ennis's marriage to Alma begets two daughters, but he remains taciturn and distant, struggling to express himself. Jack, meanwhile, marries a kind-hearted Texan woman named Lureen, with whom he has a son. However, as they assimilate into the conservative societal norms of the times, the men find it increasingly difficult to suppress their desires and the memories of that summer. The yearning for each other compels Jack to send Ennis a postcard, reigniting communication between them and potentially rekindling the old flame they thought had been extinguished by time and circumstance.