"I am back with the same account," the user known as @mujtahidd said in an email to AFP on Monday.
"The good thing is I got all my followers back," about 1.8 million of them.
He says the documents and tweets that he publishes aim for "a more just and transparent situation" in the Persian Gulf kingdom.
On Friday he said that Twitter cited the posting in April 2014 of a "private document" related to the royal family as the reason his account could no longer be accessed.
"I explained to Twitter administrators my high profile as a credible whistle-blower from within the circles of power in Saudi Arabia," he wrote from the email address that was listed with his suspended account.
He did not identify himself and said he could not be reached by telephone.
@mujtahidd added that he told Twitter it "constitutes giving in to pressure" if it merely accepted complaints regarding something he published last year.
The "whistle-blower" said Twitter did not tell him why the suspension, in effect since late last week, had been lifted.
Some of the information from @mujtahidd proved to be accurate, such as his report of King Abdullah’s death hours before the royal court made an official statement on January 23.
Abdullah was replaced by his half-brother Salman.
Twitter use is widespread in Saudi Arabia, where even King Salman has an account. Official media are tightly controlled, however.