While the celebration of Ganesh Chaturthi as a religious festival has been since time immemorial, the concept of celebrating it as a public event (Ganesh Utsav) is a relatively recent phenomenon. The history of Ganesh Utsav traces back to the early 1890s when freedom struggle in India was still in infancy and limited only among the elite club of Congress (which was formed in 1885 by the British civil servant, A.O.Hume).
It was the time when Lokamanya Tilak declared Swaraj as the national goal and sought the participation of masses but soon realized that India was deeply divided along the lines of castes. There was severe animosity among castes (especially between Brahmins & non-Brahmins) and it was high time such differences were resolved so that everybody would be united for a common cause (of freedom struggle). With these ideas in mind, Tilak hit upon the plan of gathering masses for the purpose of celebrating a festival annually which would turn forge the feeling of communal and linguistic harmony. Since Lord Ganesha was adored by people of all castes, Tilak started the tradition of Sarvajanik Ganesha Utsav where a clay idol of Ganesh would be installed in public places in Bombay. The utsav would last for several days with cultural programmes and nationalistic speeches to motivate people and interestingly even Muslim leaders would deliver speeches during such annual utsav gatherings.
As one would have expected, there was a severe backlash from orthodox groups who criticized Tilak for bringing sacred Lord Ganesh to the street and politicizing it. However, Tilak held on to his nerves and convinced them that it was just one of the means of getting people to intermingle and instill nationalistic spirit into them, which would improve the situation of the country. Using religious festival as a platform to unite Indians was a brilliant plan by Tilak because the Police (under British administration) did not have the courage to suppress religious sentiments & proceedings. In fact, the Police would not only co-operate, but also help them coordinate their activities by managing crowd, directing processions etc ,turning it into a grand success.
After witnessing the success of such public gatherings, Tilak spread the idea to towns around Bombay and subsequently to other regions of India as well. Ganesh Utsav Mandals were formed in each town to collect funds & organize such events, and by 1905, it had become a nationwide celebration.