Amnesty says the new penalties, which also apply to children, are provided for in new sections under Brunei's Sharia Penal Code and will come into effect April 3.
Brunei was the first Asian country to incorporate Islamic criminal law back in 2014.
Brunei announced in 2014 that it would implement its new penal code in three phases, gradually replacing secular law with Sharia law at the national level.
That is according to a notice on the Attorney-General's website. The fact that another of Washington's major allies - Saudi Arabia - also punishes same-sex relations by death - alongside adultery, apostasy and blasphemy - never stopped the United States from striking billions-worth of deals with Riyadh. Amnesty International, in particular, decried the introduction of "cruel and inhuman penalties" and called on the world to "urgently condemn Brunei's move to put these cruel penalties into practice".
Brunei must rowback on plans to implement changes to its penal code next month that could see LGBT+ people whipped or stoned to death for same-sex activity, human rights groups said on Monday.
Among other laws that have been introduced by Sultan Hassanal Bolkiah include the public sale of alcohol being banned, and that those who miss Friday prayers risk being fined or sent to prison. She said some of the potential offenses "should not even be deemed crimes at all, including consensual sex between adults of the same gender".
Sultan Haji Hassanal Bolkiah of Brunei shakes hands with Vietnam's President Nguyen Phu Trong.
Global organisations have called to slam such actions, asking the Sultan (Monarch) of this oil-rich nation to get laws in adherence with the worldwide standards of human rights laws.
The implementation of the law has since been delayed as officials work out the practical details under heavy opposition from rights groups.
Adoption of the other two sections of the Islamic law had been delayed five years ago due to worldwide outcry but will be now be coming into force on April 3.