The result is expected to confirm the provisional total of nearly 99% in favour of independence.
January's referendum was agreed as part of a 2005 peace deal ending more than two decades of civil war between the south and north of the country.
For many southerners, what they consider a forced union with the rest of Sudan has been a catastrophe.
The south sees itself as different in cultural, religious and ethnic terms from the north, and believes it has suffered years of discrimination.
In the last half century southerners have fought two devastating civil wars with Khartoum, in which more than two million people are estimated to have died.
So it is no surprise that the provisional results of last month's referendum showed they voted almost unanimously for separation from the north.
The announcement of the final results will not be the end of the process.
There will be tough negotiations ahead, on issues including the disputed border region of Abyei, citizenship, legal matters and resources like oil.
When Southern Sudan becomes independent in July it will face huge problems.
Though it is rich in oil, it is one of the least-developed regions on earth, and ethnic tensions and troubled relations with the north will provide constant security challenges.
But the dominant emotion for southerners once the results are announced will surely be one of huge joy.