A civil servant complained to the PCC after the Daily Mail and Independent on Sunday printed several of her tweets in which she discussed aspects of her job and made a number of comments of a political nature.
Sarah Baskerville, who works at the Department for Transport, argued that her activities on Twitter were private and she had a "reasonable expectation" that only her 700 followers would read them.
She said she had included a clear disclaimer on her Twitter feed that the views expressed there were personal, and were not representative of her employer.
But the Daily Mail and the Independent on Sunday said the account was in the public domain and could be read by anyone. They said quoting the tweets was editorially justified "in light of the requirements of the civil service code on impartiality".
In its ruling, published today, the PCC said there was no dispute that the material was open to public view and related directly to her professional life as a public servant. It concluded that there had been no invasion of privacy.
"It was quite clear that the potential audience for the information was actually much larger than the 700 people who followed the complainant directly, not least because any message could easily be retweeted to a wider audience," the ruling says.
PCC director Stephen Abell said: "As more and more people make use of such social media to publish material related to their lives, the commission is increasingly being asked to make judgements about what can legitimately be described as private information."