Wonthaggi /wɒnˈθæɡi/ is a town located 132 kilometres (82 mi) south east of Melbourne via the South Gippsland and Bass highways, in the Bass Coast Shire of Gippsland, Victoria, Australia. Known originally for its coal mining, it is now the largest town in South Gippsland, a regional area with extensive tourism, beef and dairy industries.

The name "Wonthaggi" is an Australian Aboriginal name meaning "home" from the Boonwurrung (south-central Kulin). It was used in the area some time before 1 August 1910 when the town was founded.

The Boonwurrung Aboriginal people were custodians of this stretch of coast for thousands of years prior to White settlement. The Boakoolawal clan lived in the Kilcunda area south of the Bass River, and the Yowenjerre were west of the Tarwin River along what is now the Bunurong Marine and Coastal Park. Middens containing charcoal and shellfish mark the location of their campsites along the coast.

Coal was discovered by explorer William Hovell at Cape Paterson in 1826, and was subsequently mined from the Powlett River fields in the region, between 1859 and 1864. However transporting the coal by whale boat through the surf to larger ships anchored offshore proved costly and dangerous and mining activity was soon curtailed. The coastal sands off Wonthaggi occasionally uncover the remains of ships wrecked along the coast.

A tent city was established adjacent to the Powlett River, on what were then known as the Powlett River Coalfields. The tent city had no permanent buildings and healthcare was provided by a Dr Sleeman, who was later instrumental in establishing a permanent hospital in the township of Wonthaggi, proclaimed in 1910.

Much of the coal for the colony of Victoria was sourced from Newcastle and the Hunter Valley in New South Wales, along with local supplies from private and co-operative coal mines at Outtrim, Jumbunna and Korumburra in Gippsland. After the 1909–1910 strike by coal miners in the Hunter Valley, the Victorian state government were determined to ensure stability in local supplies of coal. The State Coal Mine and the town of Wonthaggi came into being in 1910 to supply coal for the Victorian Railways. It was one of the largest and most dangerous collieries in Australia. At its peak in 1926 the mine produced 2,435 long tons (2,474 t) per day, with the Victorian Railways buying 90% of production. In 1928, Wonthaggi coal accounted for around 60% of Victorian Railways coal consumption.

A Post Office opened on 11 November 1887 in a nearby area. On 1 August 1910, this office was renamed St Clair and on the same day Powlett Coal Mine Post Office, opened earlier that year, was renamed Wonthaggi. That is when the town was given a permanent name.

Wonthaggi celebrated its centenary in 2010 and a book presenting interviews with local residents about the town history was published in 2012.