Bernacchi was born in Belgium to Italian parents, who migrated to Tasmania in 1884. His father, Angelo Bernacchi, established a vineyard on Maria Island in 1884. He was educated in Hobart, Tasmania, at the Hutchins School. He trained in astronomy at the Melbourne Observatory in the use of sextants and magnetic instruments. During this period he developed an interest in Antarctic exploration, expressed in letters to the press and by following the proceeding of Antarctic Exploration Committees.
He joined Carstens Borchgrevink's Southern Cross expedition (1898–1900) which wintered at Cape Adare, Antarctica, joining the expedition in New Zealand after the previous physicist candidate had been rejected on medical grounds. The expedition was the first to spend the winter on the Antarctic continent (the Belgian Antarctic Expedition having been first to overwinter in 1898) and the first to sledge towards the South Pole. He wrote a book about the expedition To the south polar regions: expedition of 1898-1900 published in 1900. His granddaughter Janet Crawford has edited a version of his diaries from the expedition under the title The First Antarctic Winter: The story of the Southern Cross Expedition of 1898-1900.
He was again a physicist on the Discovery expedition led by Robert Falcon Scott (1901–1904). Bernacchi was the only man on this expedition who had previously been to the Antarctic. During the trip, he made extensive magnetic observations. Following the trip, Bernacchi was awarded the Royal Geographical Society and King's Antarctic Medal as well as the Légion d'honneur. Scott was the best man at Bernacchi's marriage in 1906 in England and invited him to participate in his ill-fated second expedition but Bernacchi declined due to family commitments.
Following two short expeditions to Africa and the upper Amazon Basin in Peru, Bernacchi made two unsuccessful attempts to run for the House of Commons as a Liberal Party candidate, standing in Widnes in 1910. He also invested in rubber plantations in Malaya, Java and Borneo.
During World War I, he served subsequently in the Royal Naval Volunteer Reserve, the Admiralty and the United States Navy. In 1919, he received both an Order of the British Empire and the United States Navy Cross. Following the war, he returned to his interests in rubber.
He remained active in scientific organisations, most notably the Royal Geographical Society, serving as a council member between 1928 and 1932. Bernacchi planned his own expedition to the Antarctic in 1925, but failed to raise sufficient funds. In 1930, he organised the British Polar Exhibition and helped to organise the Second International Polar Year in 1932.
Bernacchi wrote a number of books on the Antarctic including a biography of Lawrence Oates called A Very Gallant Gentleman published in 1933 and Saga of the Discovery in 1938. In World War II, he returned to the Royal Naval Reserve Volunteers before his death in 1942.
A species of Antarctic fish, the Trematomus bernacchii was named in his honor. 
In 2001, Australia Post issued a postal stamp in honour of the 100th anniversary of Australia's involvement in Antarctic exploration. The Premier of Tasmania, Jim Bacon, unveiled sculptures of Bernacchi and fellow explorers at Sullivans Cove.
- The South polar times. London: Smith, Elder & co., 1907-1914. (Volume 2 editor.) An exact reproduction of the South polar times originally issued during the Antarctic expeditions of Robert F. Scott.
- Saga of the "Discovery". London: Glasgow, Blackie and son, Ltd.  : Re-printed by Rooster Books Ltd (2001) ISBN 9781871510225
- To the south polar regions: expedition of 1898-1900. By Louis Bernacchi; introduction by D.W.H. Walton. Denton, Harleston, Norfolk: Bluntisham Books : Erskine Press, 1991. ISBN 1-85297-035-9
- A very gallant gentleman. London: T. Butterworth, ltd. .
- That first Antarctic winter : the story of the Southern Cross Expedition of 1898-1900 as told in the diaries of Louis Charles Bernacchi / written and edited by Janet Crawford (Louis' granddaughter). Christchurch, N.Z.: South Latitude Research Ltd., in association with P.J. Skellerup, c1998. ISBN 0-473-04966-X
- Physics in Australia to 1945 - BERNACCHI, Louis Charles at www.asap.unimelb.edu.au
- Louis Bernacchi - Biographical notes at www.coolantarctica.com
- "Antarctica a sticking point". In: The Hobart Mercury, 17 May 2001 page 13.
- "Sculpting a piece of Antarctic history". In: In: The Hobart Mercury, 11 September 2002.
- "Saga of the Discovery", 1938, ISBN 1-871510-22-8
- Bernacchi the Physicist
- "Louis Bernacchi" Australian Dictionary of Biography Volume 7 Melbourne University Press published 1979 pages 275-276
- University of Melbourne biography
- "Physics in Australia to 1945" biography
- "Australian Dictionary of Biography