Nobody really knows when the festival of Ganesh Chaturthi started, but historians do tell us when it was popularized. Go back to year 1893, India was ruled by the British, the first freedom fight, the Sepoy Mutiny was crushed, India was writhing under the British Raj. The unrest against the British was growing but nothing united the different castes of India. At that time, Lokmanya Bal Gangadhar Tilak recognized the wide appeal of the deity Ganesh as "the god for everybody", and popularized Ganesh Chaturthi as a national festival in order "to bridge the gap between Brahmins and 'non-Brahmins' and find a context in which to build a new grassroots unity between them", and generate nationalistic fervor among people in Maharashtra against the British colonial rule.
Tilak encouraged installation of large public images of Ganesh in pavilions, and also established the practice of submerging in rivers, sea, or other pools of water all public images of the deity on the tenth day after Ganesh Chaturthi.
Under Tilak's encouragement, the festival facilitated community participation and involvement in the form of intellectual discourses, poetry recitals, performances of plays, musical concerts, and folk dances. It served as a meeting ground for people of all castes and communities in times when, in order to exercise control over the population, the British discouraged social and political gathering.
So Ganesh Chaturthi was popularized.
Happy Ganesh Chaturthi!
Check out this video of Ganesh Chaturthi celebrations!