He was born in Karachi, in British India (now Pakistan), to Aga Khan II and his third wife, Nawab A'lia Shamsul-Muluk, who was a granddaughter of Fath Ali Shah of Persia (Qajar dynasty).
Under the care of his mother, he was given not only that religious and Oriental education which his position as the religious leader of the Ismailis made indispensable, but a sound European training, a boon denied to his father and paternal grandfather. This blending of the two systems of education produced the result of fitting this Muslim chief in an eminent degree both for the sacerdotal functions which pertained to his spiritual position, and for those social duties required of a great and enlightened leader which he was called upon to discharge by virtue of his position. He also attended Eton and Cambridge University.
The Aga Khan traveled in distant parts of the world to receive the homage of his followers, and with the object either of settling differences or of advancing their welfare by pecuniary help and personal advice and guidance. The distinction of a Knight Commander of the Indian Empire was conferred upon him by Queen Victoria in 1897 (and later Knight Grand Commander in 1902 by Edward VII) and he received like recognition for his public services from the German emperor, the sultan of Turkey, the shah of Persia and other potentates.
In 1906, the Aga Khan was a founding member and first president of the All India Muslim League.
In 1934, he was made a member of the Privy Council and served as a member of the League of Nations (1934-37), becoming the President of the League of Nations in 1937.
He was made a "Knight of the Indian Empire" by Queen Victoria, a Grand Commander of the Indian Empire by Edward VII (1902), and a Knight Grand Commander of the Indian Empire by George V (1912).
He was an owner of thoroughbred racing horses, including a record equalling five winners of the Epsom Derby, and a total of sixteen winners of British Classic Races. He was British flat racing Champion Owner thirteen times. According to Ben Pimlott, biographer of Queen Elizabeth II, the Aga Khan presented Her Majesty with a filly called Astrakhan, who won at Hurst Park Racecourse in 1950.
In 1926, the Aga Khan gave a cup (the Aga Khan Trophy) to be awarded to the winners of an international team show jumping competition held at the annual horse show of the Royal Dublin Society in Dublin, Ireland every first week in August. It attracts competitors from all of the main show jumping nations and is carried live on Irish national television.
The Aga Khan was succeeded by his grandson Karim Aga Khan, as 'Aga Khan' and is the present Imam of the Ismaili Muslims. At the time of his death on July 11, 1957, his family members were in Versoix. A solicitor brought the will of the Aga Khan III from London to Geneva and read it before the family:
"Ever since the time of my ancestor Ali, the first Imam, that is to say over a period of thirteen hundred years, it has always been the tradition of our family that each Imam chooses his successor at his absolute and unfettered discretion from amongst any of his descendants, whether they be sons or remote male issue and in these circumstances and in view of the fundamentally altered conditions in the world in very recent years due to the great changes which have taken place including the discoveries of atomic science, I am convinced that it is in the best interest of the Shia Muslim Ismailia Community that I should be succeeded by a young man who has been brought up and developed during recent years and in the midst of the new age and who brings a new outlook on life to his office as Imam. For these reasons, I appoint my grandson Karim, the son of my own son, Aly Salomone Khan to succeed to the title of Aga Khan and to the Imam and Pir of all Shia Ismailian followers."
He is buried in Aswan, Egypt at the Mausoleum of Aga Khan.
The Official Ismaili Website
Official Website of Aga Khan Development Network