Hassanal Bolkiah, who has been sultan of Brunei since 1967, announced the change in a speech opening the Knowledge Convention, The Brunei Times reported.
"It is because of our need that Allah the Almighty, in all his generosity, has created laws for us, so that we can utilize them to obtain justice," he said.
The Guardian newspaper said Brunei is expected to introduce penalties like executing adulterers by stoning and cutting off hands of convicted thieves.
The sultan, in his speech, suggested outsiders shouldn't judge Brunei's legal code.
"We view others with clear and unhindered vision, without any form of prejudice. In return, we also have the right to expect that others will view Brunei in the same light," he said.
The country already uses Sharia but mostly for domestic matters such as inheritance and divorce. The new policy extends Sharia to criminal matters.
Local news media said only Muslims will be subject to Sharia.
Mufti Awang Abdul Aziz, a legal scholar, said Tuesday that Sharia is designed to be just for all. He said tourists shouldn't be afraid to visit Brunei.
"Do all potential tourists to Brunei plan to steal? If they do not, then what do they need to fear? Believe me when I say that with our Sharia criminal law, everyone -- including tourists -- will receive proper protection," he said.
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