Reaching the rank of lieutenant admiral (Dutch: luitenant-admiraal), he served as Minister of the Navy during World War II in the Second Gerbrandy cabinet.

[1] He served as a naval officer in the Netherlands East Indies at various times between 16 September 1908 and 1918, taking part in Dutch military expeditions in the Sunda Islands between 1905 and 1909.

[1] Furstner was promoted to commander (Dutch: kapitein-luitenant ter zee) on 14 December 1928[1] and in 1929 assumed duties as executive officer of the coastal defense ship HNLMS Jacob van Heemskerck.

[1] From 1930 to 1936, he served as director of the Hogere Marine Krijgsschool,[1] receiving a promotion to captain (Dutch: kapitein ter zee) during his tour on 27 March 1933,[1] and in that position he spread the naval theories he had developed in his studies under Castex among Royal Netherlands Navy officers attending the college.

[7] In 1932, Furstner co-founded the Alliance for National Reconstruction (Dutch: Verbond voor Nationaal Herstel, or VNH), a conservative-nationalist political party.

[7] Rather than rely on submarine ambushes as had been anticipated for 25 years, he planned to use the new battlecruisers in a more ambitious and risky version of Rambonnet's "risk theory," employing the battlecruisers in attacks on Japanese supply lines, the threat of which, in combination with the capabilities of the Royal Navy and United States Navy, he believed would deter Japan from attacks on the Netherlands East Indies.

[8] Furstner submitted a note in December 1938 about naval defense needs in the Netherlands East Indies calling for the construction of the three battlecruisers[1] and he and his supporters began openly campaigning for the adoption of his new version of a "risk theory" strategy in 1939.

[10] In a series of conferences in Singapore that began in the autumn of 1940, the Dutch met with British, American, and Australian representatives to coordinate their defense of East Asia against Japanese attack.

[13] Furstner turned his attention to leading the important work of replenishing the personnel and equipment of the Royal Netherlands Navy and preparing for the reconstruction of the Dutch naval force after the conclusion of the war.

He displayed no interest in his subordinates, to Wilhelmina′s displeasure; he never visited his men, unlike British Royal Navy officers, and did not care about Wilhelmina's criticism of him for it.

[14] When Dutch resistance members Peter Tazelaar and Gerard Dogger — who worked with Erik Hazelhoff Roelfzema and Chris Krediet in Contact Holland [nl], an effort directed by Queen Wilhelmina and the British secret service to transport agents from the United Kingdom to the Netherlands and extract people for the return journey — visited Furstner, van der Zee recounts that he was gruff and dismissive of them[15] and, when Tazelaar noted that Contact Holland's operations were by order of Queen Wilhelmina, Furstner responded that "The Queen signs the documents; we rule.

As early as 1942, he was reprimanded by the Extraordinary Court of Audit, which deemed financial expenditures he and his officers incurred in England "contrary to the necessary austerity and the impoverishment in which the Dutch people found themselves" during the German occupation of the Netherlands.

He continued to serve as Commander-in-Chief of Naval Forces until August 1945,[1] when the close of hostilities between the Allies and Japan brought World War II to an end.

[1] After World War II, Furstner was a board member of the Nationaal Comité Handhaving Rijkseenheid (English: National Committee for the Maintenance of Unity of the Kingdom), an extra-parliamentary action group in the Netherlands opposed to the independence of Indonesia.