Bacchus Marsh (Wathawurrung: Pullerbopulloke) is a town in Victoria, Australia, located approximately 50 kilometres (30 mi) north-west of the state capital Melbourne, at a near equidistance to the major cities of Melbourne, Ballarat and Geelong.

As of the 2021 census, Bacchus Marsh has a population of 7,808, while its statistical urban area (including the suburbs Darley, Maddingley, and Hopetoun Park, among others) has a population of 24,717. Bacchus Marsh is the largest urban area in the Shire of Moorabool local government area.

Traditionally a market garden area producing a large amount of the region's fruits and vegetables, in recent decades it has transformed into the main commuter town on the Melbourne–Ballarat corridor.

It was named after the colonial settler Captain William Henry Bacchus, who saw the great value of this locality as it was situated on two rivers – the Lerderderg and Werribee.

Bacchus Marsh is on the border between the Woiwurrung and Wathaurong territories of the Kulin Nation. The local clans were the Marpeang balug of the Wathaurong, and the Gunung-willam-bulluk (Wurundjeri) of the Woiwurrung. Bacchus Marsh was a meeting ground for anywhere between 150 and 400 Aboriginals even after white settlement, and corroborees were held quite regularly. While there do not appear to be any records of open hostilities between whites and indigenous people, by 1863 there were a total of only 33 Aboriginal people left in the Bacchus Marsh district, and apart from a handful of recollections of the original inhabitants preserved by pioneer settlers, little remains apart from present-day locality names, mainly of watercourses: Coimadai, Djerriwarrh, Korkuperrimul, Lerderderg, Merrimu, Myrniong, Werribee. The Wathawurrung name for the area is Pullerbopulloke with 'buluk' meaning lake.

One of the first white men to reach the Bacchus Marsh valley was pastoralist Kenneth Scobie Clarke (c. 1806–79), a native of Sutherland in Scotland. Clarke was a manager for the Great Lake Company of Van Diemen’s Land and arrived in the Port Phillip District from George Town on 25 March 1836. Captain Bacchus credited Clarke as being the first man to shear sheep in Victoria, although the Hentys had arrived in Portland with their sheep some two years earlier.

On 29 November 1836, Clarke headed west from Port Phillip with a large flock of sheep, arriving in the Bacchus Marsh district a few days later. He built a hut on the west bank of the Lerderderg River near Darley, and lived there until early 1838. According to pastoralist George Russell, Clarke had acted on information obtained from Mr Aitken, an Edinburgh man, who was most put out when he discovered that Clarke had beaten him to the Pentland Hills run.

In 1838, Englishman Captain William Henry Bacchus (1782–1849, originally of the 2nd Royal Surrey Militia) and his son William Henry Bacchus junior (1820–87) also brought sheep from Tasmania and came to the district which now bears their name. On their arrival, Clarke made an arrangement with them and ceded his run, moving to the nearby hills known as the Pentlands. The then very swampy valley was not really suitable for sheep, as they were prone to footrot. Clarke stayed in the district until 1840 or 1841, and later went to New Zealand, where he died in 1879.