Using the handle @Pontifex -- meaning "bridge builder" in Latin -- he posted: "Dear friends, I am pleased to get in touch with you through Twitter. Thank you for your generous response. I bless all of you from my heart."
"Wow! Is this true?! Pope Benedict XVI has started tweeting! Welcome Your Holliness! I'm grateful for your blessing! Follow him!" tweeted @Joyful_Minoz.
"Our Pope Benedict XVI has a twitter account! Coolest Pope in history!" wrote @alexaSaclao.
"@pontifex welcome on twitter. Glad you are now reachable to openly discuss gay marriage, birth control and gender equality!" said @wimremes.
Some are more skeptical about the pontiff's personal involvement.
"For the first time in history, a man can communicate directly with some low-level press officer in Vatican," tweeted @EsaMakinen.
A Vatican official told CNN last week that the pope would compose the tweets for the new account himself. But while the pontiff pressed the button to send his very first tweet, others are expected to send future tweets on his behalf.
The pope followed up his first message with two more tweets within minutes.
"How can we celebrate the Year of Faith better in our daily lives?" asked one.
The answer: "By speaking with Jesus in prayer, listening to what he tells you in the Gospel and looking for him in those in need."
This prompted comment that the pontiff had missed the point about social media being interactive.
"@Pontifex is answering his own tweets now. That's not really how it works, Your Holiness," said @exitthelemming.
The pope's venture into social media has also sparked a flurry of jokes.
Comedy writer Colm Tobin tweeted: "RT @Pontifex Thou shalt not covet your neighbour's Twitter followers."
"I hear he's changing it to 'thou shall not covet thy neighbour's wifi,'" was another tweeter's humorous take.
An hour after his first tweet, the pope had around 700,000 followers on his English-language account. He is also tweeting in seven other languages, including Spanish, Portuguese and Arabic.
This prompted admiration from some fellow tweeters.