The order expands the responsibilities of Interior Minister Nasir Yusuf, who was named by Abbas as his security chief earlier this year.
Yusuf continues to oversee his ministry as well as the National Security Forces, which includes elite commando units and military intelligence.
It was not immediately known who would be in charge of the general intelligence section.
Abbas' decision on Thursday is seen as a step towards meeting a key Israeli and US demand for reform.
The US and Israel have long demanded the unification of the Palestinian security services as a condition for renewing peace negotiations.
More than a dozen Palestinian security organisations have long operated as independent fiefdoms, contributing to rising lawlessness in the West Bank and Gaza Strip.