Bismillah Khan was born in a Bihari Muslim family to a Prophet Khan and Mitthan Bai in a rented house in Thatheri Bazar, Dumraon, Bihar. That morning, his father was preparing to leave the house to play the clarinet in the Prophet Bakhsh Raj Durbar that a child's ears were heard in his ears. The word Bismillah came out of his mouth with a spontaneous feeling of pleasure. He thanked Allah.
His childhood name was Kamaruddin. But he became known as Bismillah. He was the second child of his parents. The people of his family were adept at playing the darwari raga, who used to visit the Bhojpur principality of Bihar often to show their musical skills. His father used to play the clarinet in the court of Maharaja Keshav Prasad Singh of the princely state of Dumraon, Bihar. Bismillah Khan's great-grandfather Hussain Bakhsh Khan, grandfather Rasul Bakhsh, uncle Ghazi Bakhsh Khan and father Prophet Bakhsh Khan were Shehnai players. At the age of 6, Bismillah Khan came to Benares with his father. There he learned to play the clarinet from his maternal uncle Ali Baksh 'Vilayati'. His master uncle 'Vilayati' used to perform the clarinet in the Vishwanath temple.
Ustad's marriage took place at the age of 16 with Muggan Khanam, the second daughter of his maternal uncle Sadiq Ali. They gave them 9 children. He always proved to be a better husband. He loved his wife very much. But shehnai was also called her second begum. There was a family of 66 people whom they used to maintain and many times their house was also called Bismillah Hotel. Practising for 30–35 years continuously, Riyaz of six hours daily was included in his routine. After the death of Alibakhsh Mamu, Khan Saheb single-handedly transported this instrument to the heights of 60 years.
He said that this day is very special not only for him but also for all the listeners present there because Bismillah Khan is present here. Bismillah Khan also gave music for Gunj Uthi Shehnai. But at that time he was so angry that he did not give music in the second film. He often used to say that the wealth of the world on one side and music on one side would still be huge. Music cannot be beaten with money.