Sir Syed Ahmed 'Khan Bahadur' was born on 17 October 1817 to an Syed family in Delhi, which was the capital of the Mughal Empire. His family were desandants of Muhammad and then moved to the Indian subcontinent in the ruling times of Mughal Emperor Akbar–I. Many generations of his family had since been highly connected with the administrative position in Mughal Empire. His maternal grandfather Khwaja Fariduddin served as Wazir (lit. Minister) in the court of Emperor Akbar–II. His paternal grandfather Syed Hadi Jawwad bin Imaduddin held a mansab (lit. General)– a high-ranking administrative position and honorary name of "Mir Jawwad Ali Khan" in the court of Emperor Alamgir II. Sir Syed's father, Syed Muttaqi Muhammad bin Hadi Khan, was personally close to Emperor Akbar–II and served as his personal adviser.

Syed Ahmad's elder brother founded the city's first printing press in the Urdu language along with the journal Sayyad-ul-Akbar. Sir Syed pursued the study of Medicine for several years but did not complete the course. Until the death of his father in 1838, Sir Syed had lived a life customary for an affluent young Muslim noble. Upon his father's death, he inherited the titles of his grandfather and father and was awarded the title of Arif Jung by the Emperor Bahadur Shah Zafar. Financial difficulties put an end to Sir Syed's formal education, although he continued to study in private, using books on a variety of subjects. Sir Syed assumed editorship of his brother's journal and rejected offers of employment from the Mughal court.

While continuing to work as a junior clerk, Sir Syed began focusing on writing, from the age of 23 (in 1840), on various subjects (from mechanics to educational issues), mainly in Urdu, where he wrote, at least, 6000 pages. His career as an author began when he published a series of treatises in Urdu on religious subjects in 1842. He published the book Asaar-us-sanadeed (Great Monuments) documenting antiquities of Delhi dating from the medieval era. This work earned him the reputation of a cultured scholar. In 1842, he completed the Jila-ul-Qulub bi Zikr-il Mahbub and the Tuhfa-i-Hasan, along with the Tahsil fi jar-i-Saqil in 1844. These works focused on religious and cultural subjects. In 1852, he published the two works Namiqa dar bayan masala tasawwur-i-Shaikh and Silsilat ul-Mulk. He released the second edition of Ansar-as-sanadid in 1854. He also started work on a commentary on the Bible – the first by a Muslim – in which he argued that Islam was the closest religion to Christianity, with a Common lineage from Abrahamic religions. He began with Genesis and Matthew, the first books of the Old and New Testament, but quit his project before even completing those first two. His other writings such as Loyal Muhammadans of India, Tabyin-ul-Kalam and A Series of Essays on the Life of Muhammad and Subjects Subsidiary Therein helped to create cordial relations between the British authorities and the Muslim community.

Through the 1850s, Syed Ahmed Khan began developing a strong passion for education. While pursuing studies of different subjects including European jurisprudence, Sir Syed began to realise the advantages of Western-style education, which was being offered at newly established colleges across India. Despite being a devout Muslim, Sir Syed criticised the influence of traditional dogma and religious orthodoxy, which had made most Indian Muslims suspicious of British influences. Sir Syed began feeling increasingly concerned for the Future of Muslim communities. A scion of Mughal nobility, Sir Syed had been reared in the finest traditions of Muslim élite culture and was aware of the steady decline of Muslim political power across India. The animosity between the British and Muslims before and after the rebellion (Independence War) of 1857 threatened to marginalise Muslim communities across India for many generations. Sir Syed intensified his work to promote co-operation with British authorities, promoting loyalty to the Empire amongst Indian Muslims. Committed to working for the upliftment of Muslims, Sir Syed founded a modern madrassa in Muradabad in 1859; this was one of the first religious schools to impart scientific education. Sir Syed also worked on social causes, helping to organise relief for the famine-struck people of North-West Province in 1860. He established another modern school in Ghazipur in 1863.

In 1855, he finished his scholarly, well researched and illustrated edition of Abul Fazl's Ai'n-e Akbari, itself an extraordinarily difficult book. Having finished the work to his satisfaction, and believing that Mirza Asadullah Khan Ghalib was a person who would appreciate his labours, Syed Ahmad approached the great Ghalib to write a taqriz (in the convention of the times, a laudatory foreword) for it. Ghalib obliged, but what he did produce was a short Persian poem castigating the Ai'n-e Akbari, and by implication, the imperial, sumptuous, literate and learned Mughal culture of which it was a product. The least that could be said against it was that the book had little value even as an antique document. Ghalib practically reprimanded Syed Ahmad Khan for wasting his talents and time on dead things. Worse, he praised sky-high the "sahibs of England" who at that time held all the keys to all the a’ins in this world.

Sir Syed supported the British during the 1857 uprising, a role which has been criticised by some nationalists such as Jamaluddin Afghani. In 1859 Sir Syed published the booklet Asbab-e-Baghawat-e-Hind (The Causes of the Indian Revolt) in which he studied the causes of the Indian revolt. In this, his most famous work, he rejected the Common notion that the conspiracy was planned by Muslim élites, who were insecure at the diminishing influence of Muslim monarchs. He blamed the British East India Company for its aggressive expansion as well as the ignorance of British politicians regarding Indian culture. Sir Syed advised the British to appoint Muslims to assist in administration, to prevent what he called ‘haramzadgi’ (a vulgar deed) such as the mutiny.

In 1859, Syed established Gulshan School at Muradabad, Victoria School at Ghazipur in 1863, and a scientific society for Muslims in 1864. In 1875, founded the Muhammadan Anglo-Oriental College, the first Muslim university in South Asia. During his career, Syed repeatedly called upon Muslims to loyally serve the British Empire and promoted the adoption of Urdu as the lingua franca of all Indian Muslims. Syed heavily critiqued the Indian National Congress.

Having recognized the steady decline in Mughal political power, Sir Syed decided to enter the Service of the East India Company. He could not enter the English civil Service because it was only in the 1860s that natives were admitted. He did not attend the East India Company College which was not a College and did not grant degrees in law or anything else. His first appointment was as a Serestadar (lit. Clerk) at the courts of law in Agra, responsible for record-keeping and managing court affairs. In 1840, he was promoted to the title of munshi. In 1858, he was appointed to a high-ranking post at the court in Muradabad, where he began working on his most famous literary work.

Upon his transfer to Aligarh in 1864, Sir Syed began working wholeheartedly as an educator. He founded the Scientific Society of Aligarh, the first scientific association of its kind in India. Modelling it after the Royal Society and the Royal Asiatic Society, Sir Syed assembled Muslim scholars from different parts of the country. The Society held annual conferences, disbursed funds for educational causes and regularly published a journal on scientific subjects in English and Urdu. Sir Syed felt that the socio-economic Future of Muslims was threatened by their orthodox aversions to modern science and Technology. He published many writings promoting liberal, rational interpretations of Islamic scriptures. One Example was the reaction to his argument – which appeared in his tafsir (exegesis) of the Quran – that riba referred to interest charges when lending money to the poor, but not to the rich, nor to borrowers "in trade or in industry", since this Finance supported "trade, national welfare and prosperity". While many jurists declared all interest to be riba, (according to Sir Syed) this was based "on their own authority and deduction" rather than the Quran.

The onset of the Hindi-Urdu controversy of 1867 saw the emergence of Sir Syed as a champion for cause of the Urdu language. He became a leading Muslim voice opposing the adoption of Hindi as a second official language of the United Provinces (now Uttar Pradesh). Sir Syed perceived Urdu as the lingua franca of the United Provinces. Having been developed by during the Mughal period, Urdu was used as a secondary language to Persian, the official language of the Mughal court. Since the decline of the Mughal dynasty, Sir Syed promoted the use of Urdu through his own writings. Under Sir Syed, the Scientific Society translated Western works only into Urdu. The schools established by Sir Syed imparted education in the Urdu medium. The demand for Hindi, led largely by Hindus, was to Sir Syed an erosion of the centuries-old Muslim cultural domination of India. Testifying before the British-appointed education commission, Sir Syed controversially exclaimed that "Urdu was the language of gentry and Hindi that of the vulgar." His remarks provoked a hostile response from Hindu Leaders, who unified across the nation to demand the recognition of Hindi.

On 1 April 1869 he went, along with his son Syed Mahmood, to England, where he was awarded the Order of the Star of India from the British government on 6 August. Travelling across England, he visited its colleges and was inspired by the culture of learning established after the Renaissance. Sir Syed returned to India in the following year determined to build a "Muslim Cambridge." Upon his return, he organised the "Committee for the Better Diffusion and Advancement of Learning among Muhammadans" (Muslims) on 26 December 1870. Sir Syed described his vision of the institution he proposed to establish in an article written sometime in 1872 and re-printed in the Aligarh Institute Gazette of 5 April 1911:

By 1873, the committee under Sir Syed issued proposals for the construction of a college in Aligarh. He began publishing the journal Tahzib-al-Akhlaq (Social Reformer) on 24 December 1870 to spread awareness and knowledge on modern subjects and promote reforms in Muslim society. Sir Syed worked to promote reinterpretation of Muslim ideology in order to reconcile tradition with Western education. He argued in several books on Islam that the Qur'an rested on an appreciation of reason and natural law, making scientific inquiry important to being a good Muslim. Sir Syed established a modern school in Aligarh and, obtaining support from wealthy Muslims and the British, laid the foundation stone of the Muhammadan Anglo-Oriental College on 24 May 1875. He retired from his career as a jurist the following year, concentrating entirely on developing the college and on religious reform. Sir Syed's pioneering work received support from the British. Although intensely criticised by orthodox religious Leaders hostile to modern influences, Sir Syed's new institution attracted a large student body, mainly drawn from the Muslim gentry and middle classes. The curriculum at the college involved scientific and Western subjects, as well as Oriental subjects and religious education. The first chancellor was Sultan Shah Jahan Begum, a prominent Muslim noblewoman, and Sir Syed invited an Englishman, Theodore Beck, to serve as the first college principal. The college was originally affiliated with Calcutta University but was transferred to the Allahabad University in 1885. Near the turn of the 20th century, it began publishing its own magazine and established a law school. In 1920, the college was transformed into a university.

Many official translations were made of the Urdu text of The Causes of the Indian Revolt. The one undertaken by the India Office formed the subject of many discussions and debates. The pamphlet was also translated by the government of India and several members of parliament, but no version was offered to the public. A translation which had been started by a government official was finished by Sir Syed's great friend, Colonel G.F.I. Graham, and finally published in 1873.

He was appointed the fellow of the Calcutta University and Allahabad University by the Viceroy in the year 1876 and 1887 respectively.

In 1878, Sir Syed was nominated to the Viceroy's Legislative Council. He testified before the education commission to promote the establishment of more colleges and schools across India. In the same year, Sir Syed founded the Muhammadan Association to promote political co-operation amongst Indian Muslims from different parts of the country. In 1886, he organised the All India Muhammadan Educational Conference in Aligarh, which promoted his vision of modern education and political unity for Muslims. His works made him the most prominent Muslim Politician in 19th century India, often influencing the attitude of Muslims on various national issues. He supported the efforts of Indian political Leaders Surendranath Banerjee and Dadabhai Naoroji to obtain representation for Indians in the government and civil services. In 1883, he founded the Muhammadan Civil Service Fund Association to encourage and support the entry of Muslim graduates into the Indian Civil Service (ICS). While fearful of the loss of Muslim political power owing to the community's backwardness, Sir Syed was also averse to the prospect of democratic self-government, which would give control of government to the Hindu-majority population:

Sir Syed's educational model and progressive thinking inspired Muslim elites who supported the AIML. Ahmad Khan founded the All India Muhammadan Educational Conference in 1886 in order to promote Western education, especially science and literature, among India's Muslims. The conference, in addition to generating funds for Ahmad Khan's Muhammadan Anglo-Oriental College, motivated Muslim elites to propose expansion of educational uplift elsewhere, known as the Aligarh Movement. In turn this new awareness of Muslim needs helped stimulate a political consciousness among Muslim elites that went on to form the AIML.

Syed Ahmad is widely commemorated across South Asia as a great Muslim social reformer and visionary. At the same time, Syed Ahmad sought to politically ally Muslims with the British government. An avowed loyalist of the British Empire, he was nominated as a member of the Civil Service Commission in 1887 by Lord Dufferin. In 1888, he established the United Patriotic Association at Aligarh to promote political co-operation with the British and Muslim participation in the British government.

Syed Ahmed was bestowed with the suffix of 'Khan Bahadur' and was subsequently knighted by the British government in 1888 and was awarded Knight Commander of the order of Star of India (KCSI) for his loyalty to the British crown, through his membership of the Imperial Legislative Council and in the following year he received an LL.D. honoris causa from the Edinburgh University.

Sir Syed Ahmed Khan Bahadur lived the last two decades of his life in Aligarh, regarded widely as the mentor of 19th and 20th century Muslim entrepreneurs and illuminati. Battling illnesses and old age, Sir Syed died on 27 March 1898. He was buried besides Sir Syed Masjid inside the campus of the Aligarh university.

Later in his life he said, "Suppose that the English community and the army were to leave India, taking with them all their cannons and their splendid weapons and all else, who then would be the rulers of India?.... Is it possible that under these circumstances two nations—the Mohammedans and the Hindus—could sit on the same throne and remain equal in power? Most certainly not. It is necessary that one of them should conquer the other. To hope that both could remain equal is to Desire the impossible and the inconceivable. But until one nation has conquered the other and made it obedient, peace cannot reign in the land."

Aligarh Muslim University celebrated his 200th birth centenary with much enthusiasm on 17 October 2017. Former President of India shri Pranab Mukherjee was the chief guest.