Malaysia is a federation of states stretching across most of northern Borneo and the southern Malay Peninsula. Brunei, officially Brunei Darussalam, is a long-standing Sultanate composed of two discontiguous territories in northern Borneo bisected by Malaysian territory. Brunei is located on the northern coast of the island of Borneo and is encompassed entirely by the Malaysian state of Sarawak, excepting its northwestern coastlines in the South China Sea.

British imperial influence began in northern Borneo in the 19th Century, and Sarawak would expand over the next half century to enclose Brunei’s territories. In 1888, both Sarawak and Brunei became protectorates of the United Kingdom. While under British control, Brunei and Sarawak signed five boundary Agreements between 1920 and 1939, delimiting roughly half of their land boundary. Sarawak then gained independence in 1963 and became a founding member of Malaysia shortly thereafter. Brunei would not gain independence until 1984.

In 2009, the two governments completed an exchange of notes, confirming the validity of their previous boundary Agreements. A 2012 Memorandum of Understanding was then signed to begin the official boundary demarcation and land survey of the remaining undefined portions of the frontier.

As Brunei’s territory is bisected by a strip of land claimed by Malaysia, two separate segments are required to define the international boundary. The larger borderline begins in the west and totals 302 kilometers (186 miles) in length. It runs from the mouth of the Sungai Belait in a southeasterly direction until returning to the northeast toward the Brunei Bay. The second boundary, which is shorter in length, begins at the mouth of the Sungai Pandaruan and follows the river before eventually turning east, and returns north to its terminal point in the Brunei Bay, extending for 251 kilometers (156 miles). The process of demarcating the remaining sections of the boundary began in 2014 and, as of 2024, the work is ongoing.

While the methods for determining the boundary between Brunei and Malaysia have been settled, a conflict remains over the Limbang River Valley. Brunei has a long-standing claim to Limbang, the area of Sarawak dividing Brunei’s two territories. This dispute has historically been a source of tension between the two States, but it has lessened in recent years as Brunei and Malaysia collaborate to negotiate their frontiers.

Brunei and Malaysia also have an established maritime boundary.