Nasir Husain Khan was born in Bhopal, India. He was the fourth of five children born to Jaffar Husain Khan, a history teacher, and Aamna, a housewife. He grew up a mischievous child in an orthodox family that looked down on films and theatrical works. Nevertheless, Nasir found himself working on skits in the local area, much to the dismay of his family. He was also an avid reader. His father died when he was a teenager, which allowed him to pursue his interest in the arts more freely. He moved to Lucknow where he earned his BA degree. He wrote many short stories and radio plays and occasionally performed in them. He won a first-prize for a short story that he had submitted to a Urdu magazine "Aaj Khal". (He would much later adapt it into the stark drama Baharon Ke Sapne (1967)). He worked as a secretary for a year before moving to Bombay where he met people in the film industry. He told film producer Sasadhar Mukherjee about his writing credentials, who then hired him for his Filmistan studios. He was there for a decade writing films, such as Chandni Raat (1949), Shabnam (1949), Shabistan (1951), Shart (1954). He had a huge hit with history drama Anarkali (1953), but it was comedies Munimji (1955) and Paying Guest (1957) that started bringing him attention. It was on Munimji (1955) that he met an assistant choreographer named Margaret Francina Lewis. They fell in love and married, and she changed her name to Ayesha Khan, and they would have two children: Mansoor Khan and Nuzhat Khan. S. Mukherji gave him a chance to direct a comedy that Husain wrote titled Tumsa Nahin Dekha (1957). The lighthearted musical made a box-office star out of Shammi Kapoor, and cemented Husain's career as a writer and director, when the film became a big hit. The film set the foundation for his future films, that of a happy-go-lucky hero who woos the heroine by singing catchy songs and defeats the villain, and then the hero and heroine live happily ever after. He cast Kapoor again in Dil Deke Dekho (1959), which introduced a former child actress named Asha Parekh as the heroine. The film made a star out of Parekh and she remained Husain's heroine in his next six productions: Jab Pyar Kisise Hota Hai (1961), Phir Wohi Dil Laya Hoon (1963), Teesri Manzil (1966) (Husain wrote and produced, but Vijay Anand directed and edited the film), Baharon Ke Sapne (1967), Pyar Ka Mausam (1969), and Caravan (1971)(Husain brought in his younger brother Tahir Hussain to produce). Most of these films were hits, but the married Husain also started a romantic relationship with Parekh that lasted decades. Neither divorce nor bigamy were options, since it would have wreaked havoc on both their families. They also didn't break up, since their professional association made both of them rich and famous. Asha remained faithful to Husain by never marrying anyone else and called him the "one and only true love" of her life. Knowing that Asha won't be a heroine forever, he got her involved in a film distribution company called "Movie Gems", where they distributed 21 films. He moved onto casting other heroines in Yaadon Ki Baaraat (1973) and Hum Kisise Kum Naheen (1977), and both films were hits, but after the latter film, he and Asha decided to close up Movie Gems. Hussain then directed his first flop Zamaane Ko Dikhana Hai (1981). Undeterred, he directed his next film Manzil Manzil (1984) and brought back Asha for a small cameo in the mother role, but the film still flopped. As did his next film Zabardast (1985), which turned out to be his last directorial venture. He then handed the reins over to his son Mansoor Khan to direct Qayamat Se Qayamat Tak (1988), which starred his nephew Aamir Khan, which became a big hit. Since Nasir wrote the script, he won the Filmfare Best Screenplay Award. He would win the Filmfare Best Movie Award for producing Mansoor's directorial effort Jo Jeeta Wohi Sikandar (1992), which again starred his nephew Aamir Khan. The final film he wrote was Akele Hum Akele Tum (1995). He won a special Filmfare Award for his contribution to Hindi cinema in 1996, and the Zee Cine Lifetime Achievement Award in 2000. His wife died in 2001. Asha Parekh chose not to visit him anymore. She also didn't propose marriage to the widowed Husain, since he had become a shadow of his former self. But she stayed in touch with him by phone. He died of a heart attack on March 13, 2002. A devastated Asha attended his funeral, and she later wrote about their love story in her 2017 memoir "The Hit Girl". Husain's family, including his daughter Nuzhat Khan, grandson Imran Khan, and nephew Aamir Khan attended the book's launch to show support for Asha. Both their families remain close to each other.