Hassanal Bolkiah became the Sultan of Brunei Darussalam on 5 October 1967, after his father abdicated.

On 1 January 1984, Brunei became independent from the United Kingdom after nearly 20 years of being a protectorate. Hassanal Bolkiah recited the Declaration of Independence at midnight, assuming control of Brunei as an independent country under a 'democratic' monarch.

In connection with the Silver Jubilee Celebration of Sultan Hassanal Bolkiah assuming the throne on 5 October 1992, he ordered the creation of a foundation called the Sultan Haji Hassanal Bolkiah Foundation.

In 1997, Shannon Marketic sued Jefri Bolkiah, Prince of Brunei and younger brother of Hassanal Bolkiah, claiming that she and other women were hired for promotional work but instead held as a 'virtual prisoner', drugged and sexually abused. The sultan denied the claims, and the lawsuit was eventually dismissed.

Sultan of Brunei was given the titles of Honorary Admiral of the Royal Navy and Honorary General of the British Army by Queen Elizabeth II during his participation in an event at Britannia Royal Naval College, Dartmouth.

In 2003, Hassanal Bolkiah divorced Mariam Abdul Aziz, a former flight attendant for the national carrier, Royal Brunei Airlines, and stripped her of all her royal titles.

On 27 January 2005, Sultan Hassanal Bolkiah was awarded an Honorary Doctor of Laws by the National University of Singapore.

During his visit to the Pakistan Army's SSG headquarters at Cherat, Sultan of Brunei was awarded the rank of Honorary Colonel Commandant of Pakistan's Special Service Group (SSG).

On 9 March 2006, the Sultan amended Brunei's constitution to make himself infallible under Bruneian law, granting himself full executive authority and emergency powers since 1962.

During his state visit to the Philippines, Sultan of Brunei was awarded the Order of Lakandula Grand Collar by President Gloria Macapagal Arroyo.

In 2010, Hassanal Bolkiah divorced Azrinaz Mazhar Hakim, a former Malaysian TV3 presenter, and stripped her of all titles, honours, and monthly allowance.

On 14 April 2011, Sultan Hassanal Bolkiah was conferred the Honorary Doctorate of Law by King's College London.

On 21 April 2011, Sultan Hassanal Bolkiah received an honorary doctorate in philosophy and humanities from Universitas Indonesia.

In January 2013, the Royal College of General Practitioners designated the sultan the first Companion of the college for services to healthcare in Brunei and abroad.

In 2014, Hassanal Bolkiah declared the implementation of strict Islamic criminal penalties in Brunei, including flogging, amputation of limbs, and death by stoning. This move prompted rare domestic opposition and worldwide outrage.

On 9 February 2015, Sultan Hassanal Bolkiah led his team to victory in the Richard Mille Exhibition Polo Match, where the black team of the monarch defeated the white team 7-5 on the eighth day of the four-team charity competition at the Royal Brunei Polo and Riding Club in Jerudong to advance to the final.

On 22 October 2015, Hassanal Bolkiah appointed himself as the country's Minister of Foreign Affairs, replacing his younger brother Prince Mohamed Bolkiah.

In 2015, Hassanal Bolkiah banned public celebrations of Christmas in Brunei, including wearing hats or clothes that resemble Santa Claus. The ban only affected local Muslims, while Christians were still allowed to celebrate Christmas.

On 5 October 2017, Bolkiah celebrated his Golden Jubilee to mark the 50th year of his reign.

On 23 March 2019, Sultan Hassanal Bolkiah was conferred the Honorary Doctorate Islamic Leadership from Universiti Teknologi MARA (UiTM), Malaysia.

As Prime Minister, Hassanal Bolkiah implemented a Sharia law penal code in Brunei in April 2014, which included harsh punishments such as death by stoning, severing of limbs, and flogging for crimes including abortion, adultery, and same-sex sexual acts. This sparked international protests and calls for boycotts of companies owned by the Brunei Royal Family.

On 17 April 2019, Sultan Hassanal Bolkiah's Honorary Doctor of Letters degree from the University of Aberdeen, Scotland, was revoked.

On 6 May 2019, Sultan Hassanal Bolkiah's Honorary Doctor of Law degree from the University of Oxford, England, was returned following a letter from the University, but not revoked.