Coulson, editor of the now defunct News of the World newspaper from 2003-2007, was convicted last week of conspiracy to intercept voicemails on mobile phones following a high-profile eight-month trial at London's Old Bailey court.
The prime minister, who has apologised for having hired Coulson, said of the sentence: "What this says is that it's right that justice should be done and that no one is above the law. Opposition leader Ed Miliband has criticised Cameron for bringing a criminal into the heart of Downing Street.
The maximum sentence the 46-year-old could have faced was two years but the judge said he had taken into account Coulson's good character. He showed no reaction as the sentence was read out in a packed Court.