The film opens during the 1960 Summer Olympics in Rome, where the coach passionately exclaims, > "Bhaag Milkha Bhaag!" This phrase serves as a powerful reminder of the haunting childhood memories of Milkha Singh, portrayed by Farhan Akhtar, that overshadowed his early racing career and led to a disheartening fourth-place finish. The turmoil of the 1947 Partition of India brings chaos and mass religious violence to Punjab, tragically resulting in the deaths of Milkha's parents.
Relocating to Delhi, he eventually reunites with his sister. As he navigates life in impoverished refugee camps, he finds companionship in fellow refugees and learns to survive through petty theft. Amid this struggle, he falls in love with Biro (Sonam Kapoor), who encourages him to embrace a life of integrity. It is in the army that Milkha catches the attention of a Havaldar after triumphing in a race that promises milk and eggs as rewards, which leads to his selection for a commission.
However, on the eve of the Indian team's selection for the Olympics, he faces ridicule and violence from senior competitors he had previously outpaced. Despite being injured, he perseveres and breaks the national record in the race, returning home as a national champion to propose to Biro, only to discover that she has been married off while he was away.
During the 1956 Melbourne Olympics, he becomes involved with the granddaughter of his Australian technical coach, leading to a regretful one-night stand that results in a dismal performance in his final race. Overcome with guilt, he punishes himself and reflects on his shortcomings. On his journey back to India, he learns from his coach that the world record for the 400m race stands at 45.90 seconds. With a renewed sense of purpose, he trains rigorously, subsequently achieving an astounding 45.80 seconds at the Asian Games in Tokyo in 1958.
Prime Minister Jawaharlal Nehru persuades him to head the Indian team for a friendly race in Pakistan. Unfortunately, he becomes distracted, missing important press events, but his painful past resurfaces when he visits his village and recalls the traumatic murder of his parents, along with his father's final words, "Bhaag Milkha Bhaag!" Through this emotional turmoil, he finds solace in a boy who turns out to be the son of his childhood friend.
When the race begins, although the Pakistani favorite initially leads, Milkha steadily overtakes his competitors, ultimately clinching victory and gaining the respect of both nations. Impressed by his incredible performance, General Ayub Khan, the Pakistani president, bestows upon him the title of "The Flying Sikh." In a gesture that highlights his legacy, Nehru proclaims a day in Milkha's honor as a "National Holiday," fulfilling the wishes of the man who overcame immense adversity.
