She occasionally cast glances at her husband who is in the dock accused of helping her to hide evidence from police.
"My mum says I told her when I was eight I wanted to be a journalist," she said, before noting to the judge that mothers tend to say that sort of thing.
The jury was told she moved to the News of the World to work on its magazine as a researcher in 1989, and later as a writer. Asked how good she was at interviewing people for stories, she said: "Well I kept my job so I must have been alright."
Despite a lack of experience and only basic journalism training, the court heard how she rapidly rose through the ranks. By March 1994, she was deputy features editor and the following September, at the age of just 27, was made acting deputy editor of what was then Britain's biggest selling newspaper.
(Read more: Ex-News Corp execs hauled to trial in hacking case)
Brooks, 45, is still accused of four other offences relating to conspiracy to hack voicemail messages on mobile phones, authorising illegal payments to public officials and then plotting to hinder a subsequent police investigation.
Before she began her defence, the jury were instructed by the judge overseeing her trial at London's Old Bailey court to return a verdict of not guilty on one of two charges against her of conspiracy to commit misconduct in a public office.
This related to an allegation that Brooks had approved an illegal 4,000-pound ($6,700) payment for a picture of Prince William dressed as a "James Bond girl" and wearing a bikini while at a military academy party in 2006.
"I have decided there is no case for Mrs Brooks to answer on count four, that is the charge relating to the picture of Prince William in a bikini that was acquired by the Sun newspaper," the judge, Justice John Saunders told the jury.
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