De Jong applied at the Royal Naval College in Den Helder and graduated as an ensign in the Navy and joined the Submarine Service.

After the 1959 general election, De Jong was unexpectedly appointed as State Secretary for Defence tasked with Naval Affairs taking office on 25 June 1959.

After the 1963 general election, De Jong was appointed as Minister of Defence in the Marijnen cabinet taking office on 24 July 1963.

[10][11][12] Petrus Jozef Sietse de Jong was born on 3 April 1915 in Apeldoorn in the Netherlands province of Gelderland in a Roman Catholic family that originated from Friesland, as the sixth of seven children of Joännes Jans de Jong (24 February 1878 – 28 November 1931), a railroad superintendent, and Gijsberta Adriana Schouten (29 December 1877 – 30 June 1957).

De Jong successfully navigated the HNLMS O 24 through English Channel and was awarded the Bronze Cross for bravery on 16 July 1940.

Following the end of World War II De Jong continued to serve in the Royal Netherlands Navy holding several administrative functions.

In October 1958 De Jong was promoted to captain and appointment as commanding officer of the destroyer HNLMS Gelderland.

It was the second time that De Jong was asked for a political office, for the Dutch general election of 1956 he was approached by Carl Romme the leader of the Catholic People's Party for a seat in the House of Representatives but De Jong respectfully declined his offer, and stated: "I don't have political ambitions, I want to become an admiral".

[15] Immediately thereafter, De Jong served as Minister of Defence in the successive Marijnen, Cals and Zijlstra cabinets.

His cabinet was confronted with a demand for democratic reforms in the society and it decided to democratise colleges and universities after the famous Maagdenhuisbezetting.

Meanwhile, a pay pause due to the decision of employers and employees to raise wages was partly revoked after anti-government demonstrations and strikes.

Internationally, relations with Indonesia improved, resulting in a visit by president Suharto which was, however, overshadowed by the occupation of the Indonesian embassy by Moluccans.

Following the end of his active political career, De Jong occupied many posts in industry and seats on numerous supervisory boards.

On 25 March 2010, De Jong, still visibly spirituous and active, gave a speech at Nieuwspoort about the publication of the biography of former Minister of Foreign Affairs and the 5th Secretary General of NATO Joseph Luns.

In an episode of the Dutch television programme Netwerk aired in 2005, he is even labelled as perhaps the best postwar Prime Minister of the Netherlands.

[27] Former Member of the Senate and Righteous Among the Nations Johan van Hulst said that of all the prime ministers he worked with in twenty-five years, De Jong was the best.

[28] On 23 March 2011, the history channel Hollanddoc devoted an episode about his life with the quote "Attention for the least-known prime minister after World War II, but perhaps the most successful: Piet de Jong"[29] In November 2011, the second edition of his in 2001 released biography Van buitengaats naar Binnenhof.

"[30] De Jong said to Queen Juliana, for whom he had served as aide-de-camp, when he was sworn in as State Secretary for Defence, "Majesty, there you see how a person comes down in the world."

(Dutch: "Majesteit, zo ziet u maar hoe een mens aan lager wal kan raken.")

Anneke Bartels died on 6 January 2010 two days before her ninety-fifth birthday after suffering from heart and lung illnesses since 2000.

[citation needed] De Jong was the second oldest Prime Minister of the Netherlands by age after Willem Drees who lived to 101 years, 314 days.