A spokesman said Pope Benedict XVI wanted to "reach out to everyone" with tweets translated into eight languages.
The first tweet from his account, whose name means both pontiff and builder of bridges, is expected on 12 December.
Last year, the Pope sent his first tweet last year from a Vatican account to launch the Holy See's news information portal.
"We are going to get a spiritual message. The Pope is not going to be walking around with a Blackberry or an iPad and no-one is going to be putting words into the Pope's mouth," Greg Burke, senior media advisor to the Vatican said.
"He will tweet what he wants to tweet," he added, though the leader of the world's 1.2 billion or so Roman Catholics is expected to sign off, rather than write, each individual tweet himself.