Tilak was born at Chummakachu Lane (Ranjani Aaleea) in Chikhalgaon, Ratnagiri, Maharashtra, to a Chitpavan Brahmin family. His father was a famous schoolteacher and a Sanskrit scholar who died when Tilak was sixteen. His brilliance rubbed off on young Tilak, who graduated from Deccan College, Pune, in 1877. Tilak was among one of the first generation of Indians to receive a college education.

Tilak was expected, as was the tradition then, to actively participate in public affairs. He believed that “Religion and practical life are not different. To take to Sanyasa (renunciation) is not to abandon life. The real spirit is to make the country your family instead of working only for your own. The step beyond is to serve humanity and the next step is to serve God.” This dedication to humanity would be a fundamental element in the Indian Nationalist movement.

After graduating, Tilak began teaching mathematics in a private school in Pune. Later due to some ideological differences with the colleagues in the New School, he decided to withdraw from that activity. About that time he became a journalist. He was a strong critic of the Western education system, feeling it demeaned the Indian students and disrespected India's heritage. He organized the Deccan Education Society with a few of his college friends, including Gopal Ganesh Agarkar, Mahadev Ballal Namjoshi and Vishnu Krishna Chiplunkar whose goal was to improve the quality of education for India's youth. The Deccan Education Society was set up to create a new system that taught young Indians nationalist ideas through an emphasis on Indian culture. Tilak began a mass movement towards independence that was camouflaged by an emphasis on a religious and cultural revival. He taught Mathematics at Fergusson College.

Tilak joined the Indian National Congress in 1890. He opposed its moderate attitude, especially towards the fight for self government. He was one of the most eminent radicals at the time.

In 1891 Tilak opposed the Age of Consent bill. The act raised the age at which a girl could get married from 10 to 12. The Congress and other liberals supported it, but Tilak was set against it, terming it an interference with Hinduism. A plague epidemic spread from Mumbai to Pune in late 1896, and by January 1897, it reached epidemic proportions. In order to suppress the epidemic and prevent its spread, it was decided to take drastic action, accordingly a Special Plague Committee, with jurisdiction over Pune city, its suburbs and Pune cantonment was appointed under the Chairmanship of W.C. Rand, I.C.S, Assistant Collector of Pune by way of a government order dated 8 March 1897. Tilak took up the people's cause by publishing inflammatory articles in his paper Kesari, quoting the Hindu scripture, the Bhagavad Gita, to say that no blame could be attached to anyone who killed an oppressor without any thought of reward. Following this, on 22 June, Rand and another British officer Lt. Ayerst were shot and killed by the Chapekar brothers and their other associates. Tilak was charged with incitement to murder and sentenced to 18 months' imprisonment. When he emerged from prison, he was revered as a martyr and a national hero and adopted a new slogan, "Swaraj (Self - Rule) is my birth right and I shall have it."

Following the partition of Bengal in 1905, which was a strategy set out by Lord Curzon to weaken the nationalist movement, Tilak encouraged a boycott, regarded as the Swadeshi movement.

Tilak opposed the moderate views of Gopal Krishna Gokhale, and was supported by fellow Indian nationalists Bipin Chandra Pal in Bengal and Lala Lajpat Rai in Punjab. They were referred to as the Lal - Bal - Pal triumvirate. In 1907, the annual session of the Congress Party was held at Surat (Gujarat). Trouble broke out between the moderate and the extremist factions of the party over the selection of the new president of the Congress. The party split into the "Jahal matavadi" ("Hot Faction," or extremists), led by Tilak, Pal and Lajpat Rai, and the "Maval matavadi" ("Soft Faction," or moderates). The radicals like Aurobindo Ghose were Tilak supporters.

On 30 April 1908 two Bengali youths, Prafulla Chaki and Khudiram Bose, threw a bomb on a carriage at Muzzafarpur in order to kill the Chief Presidency Magistrate Douglas Kingsford of Calcutta fame, but erroneously killed some women travelling in it. While Chaki committed suicide when caught, Bose was tried and hanged. Tilak in his paper Kesari defended the revolutionaries and called for immediate Swaraj or Self - rule. The Government swiftly arrested him for sedition. He asked a young Muhammad Ali Jinnah to represent him. But the British judge convicted him and he was imprisoned from 1908 to 1914 in the Mandalay Prison, Burma. While imprisoned, he continued to read and write, further developing his ideas on the Indian Nationalist movement. While in the prison he wrote the famous "Gita Rahasya", lots of copies of which were sold and the money was donated for the freedom fighting.

Much has been said of his trial of 1908, it being the most historic trial. His last words on the verdict of the Jury were: "In spite of the verdict of the Jury, I maintain that I am innocent. There are higher powers that rule the destiny of men and nations and it may be the will of providence that the cause which I represent may prosper more by my suffering than by my remaining free". These words now can be seen imprinted on the wall of Room. No. 46 at Bombay High Court.

Tilak had mellowed after his release in June 1914, more because of the diabetes and hardship in Mandalay prison. When World War I started in August, Tilak, cabled the King - Emperor in Britain of his support and turned his oratory to find new recruits for war efforts. He welcomed The Indian Councils Act, popularly known as Minto - Morley Reforms which had been passed by British parliament in May 1909 terming it as ‘a marked increase of confidence between the Rulers and the Ruled’. Acts of violence actually retarded than hastened the pace of political reforms, he felt. He was eager for reconciliation with Congress and had abandoned his demand for direct action and settled for agitations ‘strictly by constitutional means’ - a line advocated by his rival Gopal Krishna Gokhale. Tilak saw the spark in Gandhi and tried his best to convince Gandhi to leave the idea of "total Ahimsa" and try to get "Swarajya" by all means. Gandhi though looked upon him as his guru, did not change his mind.

Later, Tilak re-united with his fellow nationalists and re-joined the Indian National Congress in 1916. He also helped found the All India Home Rule League in 1916 - 18 with Joseph Baptista, Annie Besant, G.S. Khaparde and Muhammad Ali Jinnah. After years of trying to reunite the moderate and radical factions, he gave up and focused on the Home Rule League, which sought self rule. Tilak travelled from village to village trying to conjure up support from farmers and locals to join the movement towards self rule. Tilak was impressed by the Russian Revolution, and expressed his admiration for Lenin.

Tilak, who started his political life as a Maratha protagonist, during his later part of life progressed into a prominent nationalist after his close association with Indian nationalists following the partition of Bengal. When asked in Calcutta whether he envisioned a Maratha type of government for Free India, Tilak replied that the Maratha dominated Governments of 17th and 18th centuries were outmoded in 20th century and he wanted a genuine federal system for Free India where every religion and race were equal partners. He added that only such a form of Government would be able to safeguard India's freedom. He was the first Congress leader to suggest that Hindi written in the devanagari script, should be accepted as the sole national language of India.

In 1894, Tilak transformed household worshipping of Ganesha into Sarvajanik Ganeshotsav and he also made Shiva Jayanti (birth anniversary celebrations of Chhatrapati Shivaji Maharaj) as a social festival. It is touted to be an effective demonstration of festival procession. Gopal Ganesh Agarkar was the first editor of Kesari, a prominent Marathi weekly in his days which was started by Lokmanya Tilak in 1880 - 81. Gopal Ganesh Agarkar subsequently left Kesari out of ideological differences with Bal Gangadhar Tilak concerning the primacy of political reforms versus social reforms, and Gopal Ganesh Agarkar started his own periodical Sudharak. He often said, "I regard India as my Motherland and my Goddess, the people in India my kith and kin, and loyal and steadfast work for their political and social emancipation my highest religion and duty"

In 1903, he wrote the book The Arctic Home in the Vedas. In it he argued that the Vedas could only have been composed in the Arctics, and the Aryan bards brought them south after the onset of the last Ice age. He proposed a radically new way to determine the exact time of Vedas. He tried to calculate the time of Vedas by using the position of different Nakshatras. Positions of Nakshtras were described in different Vedas.

Tilak also authored 'Shrimadbhagwadgeetarahasya' - the analysis of 'Karmayoga' in the Bhagavadgita, which is known to be the gist of the Vedas and the Upanishads.