Overbeck was the son of pharmacist and medical councillor Georg Heinrich Overbeck from Lemgo. He came to Bremen for a commercial apprenticeship with his uncle in the family business there, but did not stay long, and emigrated to the United States in the spring of 1850 with his cousin August Meier. He went to San Francisco and opened a business, while undertaking adventurous trade journeys to Hawaii, the South Seas, Alaska, and the Bering Strait.
He came into contact with the English trading house Dent & Co., which in 1854 gave him a job in British Hong Kong. There, he had four children with a Chinese woman named Lam Tsat-Tam. They were Lily Overbeck, Oi Mond Overbeck, Annie Overbeck and Victoria Overbeck. In 1856, he was appointed as Prussian Vice Consul before becoming a consul for the Austrian Empire in 1864. Following the Austro-Prussian War, Overbeck resigned from his Prussian post in 1866. Towards the end of the war, his position as the consul for the Austrian was elevated to aristocracy in 1867. A survey took place in the Austrian territory in 1873.
In January 1876, he purchased from Joseph William Torrey for $15,000 the concessionary rights of American Trading Company of Borneo to territories in northern Borneo, conditional on successful renewal of the concessions from local authorities. Overbeck was appointed Maharaja of Sabah and Rajah of Gaya and Sandakan in a 29 December 1877 treaty with Brunei Sultan Abdul Momin, who still claimed ownership of northern Borneo. In the same year, Overbeck founded a joint venture (known as Dent & Overbeck Company/Overbeck & Co.) with the British brothers of Alfred and Edward Dent as financiers.
From November 1877, he undertook an expedition to Borneo with an American steamer for the acquisition of territorial rights and exploitation of mineral resources in the territory. Following his expedition, he met with the Sultan of Sulu and forged a second treaty with Sultan Jamalulazam of Sulu, who titled him Dato Bendahara and Raja Sandakan on 22 January 1878. The far-reaching concession attracted great attention in Europe and the United States; The Washington Post described it as the most important transfer obtained by a commercial company since the days of the British East India Company.
But on 22 July 1878, the Spanish forces operating from the Philippines forced the Sultan of Sulu to surrender, causing Overbeck to lose his title and territory in the north-eastern areas just gained from the Sultan. Overbeck then returned to Europe from 1879–80 to seek support for enforcement of the concession agreement, and to promote the territory to Austria-Hungary and the Kingdom of Italy. As Great Britain had a strong interest in Borneo, Overbeck managed to gain support from that country while in his home country only Alexander Georg Mosle supported his bid to acquire the territory as part of the German Empire.
At the beginning of 1881, the British North Borneo Provisional Association Limited was established after Overbeck transferred its rights to the Dent brothers. The company succeeded in pushing back the Spanish claim within a year and in establishing the territory as a British protectorate known as North Borneo. The interpretation of the Jawi concession documents of 1877–78 still plays a role in the international dispute between the modern states of Malaysia and the Philippines regarding territorial claims in the northern Borneo (presently known as Sabah).
In 1870 Overbeck married Romaine Madeleine Goddard (1847–1926). Her father, already deceased, was Daniel Convers Goddard (1822–1852), the first Assistant Secretary in the United States Department of the Interior; her mother Madeleine Vinton Dahlgren (1825–1889), daughter of the Congressman Samuel F. Vinton, was a valued author who married the admiral John A. Dahlgren in 1865 in a second marriage. The wedding of Overbeck and Romaine Goddard on 16 March 1870 was a social event in Washington, D.C., attended by President Ulysses S. Grant, his wife Julia Grant, Chief Justice Salmon P. Chase, and numerous ambassadors.
The couple had three sons: Baron Gustav Convers von Overbeck, Baron Oscar Karl Maria von Overbeck and Baron Alfred von Overbeck (1877–1945). Romaine was an excellent pianist and often lived with her family in Washington during her husband's journeys; In December 1875, she was presented by Kurd von Schlözer at the German Embassy in Washington, and began a brief violent affair with Hans von Bülow. Relying financially on the income of a family trust from coal mines, she later lived apart from her husband in Baden-Baden and Berlin. Little is known about Overbeck's life since then. Overbeck died at the age of 64 in London.
- 1862: Prussian Order of the Crown, 4th Class
- 1864: Order of the Iron Crown 3rd Class
- 1867: Commander's Cross of the Order of Franz Joseph
- Rainer Pape: Gustav Freiherr von Overbeck (1830–1894). Eine biographische Skizze, in: Lippische Mitteilungen aus Geschichte und Landeskultur (in German) 28 (1959) 163–217
- Volker Schult (2008). Wunsch und Wirklichkeit: deutsch-philippinische Beziehungen im Kontext globaler Verflechtungen 1860-1945 (in German). Logos Verlag Berlin GmbH. pp. 51–53. ISBN 978-3-8325-1898-1.
- Rozan Yunos (7 March 2013). "Sabah and the Sulu claims". The Brunei Times. Archived from the original on 17 June 2014. Retrieved 20 September 2013.
- Rozan Yunos (21 September 2008). "How Brunei lost its northern province". The Brunei Times. Archived from the original on 17 June 2014. Retrieved 28 October 2013.
- Maharaja being an unusual title for this place and time, its use may reflects self-aggrandizement by Overbeck; see: P. J. Rivers, "The Origin of 'Sabah' and a Reappraisal of Overbeck as Maharajah", Journal of the Malaysian Branch of the Royal Asiatic Society 77(1), 2004; pp. 79–80. "It is a rarity in the Malay World except as an honorific Sri Maharajah. Thus, while Torrey's appointment was also as 'Supreme Ruler', the American only styled himself 'Rajah Torrey' in 1876 in Hong Kong where he was well known but 'in very bad repute'. Overbeck also was bestowed with several positions as Rajah but, using upper case as a 'Supreme Ruler', opted for the title of 'Maharajah of Sabah', which seems unwarranted on several accounts."
- Nicholas Tarling, Imperialism in Southeast Asia: 'A fleeting, passing phase'.; London: Routledge, 2001; p. 63.
- Geoffrey Marston (1967). "International Law and the Sabah Dispute: A Postscript" (PDF). Australian International Law Journal. Retrieved 14 May 2017.
- "Madeleine Vinton Dahlgren Papers Folder Listing". Box: 1 Fold: 2 Scrapbook. Georgetown University Library. Archived from the original on 3 September 1999.
Untitled news item reporting on the voyage of the Baron de Overbeck in the steamship America and of his being conferred the title of Maharajah of Sabah by the Sultan of Borneo, after concluding successful negotiations for the cession of territory to the former's London-based company. Part of this land had formerly been ceded to the American Trading Company. Of Overbeck's achievement, the article states: "...this cession is one of the greatest secured by a commercial company since the days of the famous East India Company..." (Washington Post, April 12, 1878)
- Robert Fitzgerald (7 January 2016). The Rise of the Global Company: Multinationals and the Making of the Modern World. Cambridge University Press. pp. 75–. ISBN 978-0-521-84974-6.
- British North Borneo Chartered Company (1878). "British North Borneo company charter". Internet Archive. Retrieved 14 May 2017.
- Madeleine Vinton Dahlgren (1882). Memoir of John A. Dahlgren, Rear-admiral United States Navy. J. R. Osgood.
- R. Allen Lott (6 February 2003). From Paris to Peoria: How European Piano Virtuosos Brought Classical Music to the American Heartland. Oxford University Press. pp. 341–. ISBN 978-0-19-534889-7.
- Alan Walker (4 December 2009). Hans von Bülow: A Life and Times. Oxford University Press. ISBN 978-0-19-970938-0.