The decree, published by the official SPA news agency and other media organisations in Saudi Arabia, says that the committee's members must be the sons or grandsons of Abdul Aziz bin Saud, the kingdom's founder who died in 1953.
The succession law, which does not apply to King Abdullah, who is in his mid-80s, or to his half-brother Crown Prince Sultan, "aims at streamlining the succession process," the English-language Arab News said.
The transfer of power in Saudi Arabia, founded in 1932, is keenly watched by oil markets as the vast nation sits on one quarter of the world's known reserves.
Saudi Arabia is an absolute monarchy with no elected parliament or political parties and the population of about 23 million is ruled according to Sharia, Islamic law.
The succession law, which was announced in October 2006, establishes a new mechanism for declaring the reigning monarch or heir to the throne unfit to continue in their duties, either temporarily or permanently.
On the death of the monarch, the committee would immediately hold a meeting to name the crown prince as king and then the new ruler would have 10 days to inform the commission of his choice of crown prince.
Western diplomats have welcomed efforts to regulate succession in the Islamic kingdom, which they say is an attempt to avoid the leadership disputes which have erupted in the past.
In 1964, the founder's eldest son King Saud was deposed by his brother Faisal, who was then assassinated in 1975.