Mr Shayler, 36, was greeted by his girlfriend and brother as he left Ford open prison, near Arundel, West Sussex, yesterday after serving less than seven weeks in jail.
He was found guilty on three charges of breaching the act and sentenced to six months in jail in November.
In a statement issued by his solicitor, Mr Shayler said he would be appealing to the Court of Appeal and taking his case to the European Court of Human Rights.
Mr Shayler, who is 37 todayOK, will spend another seven weeks under the British Home Office's home detention curfew scheme.
He will have to observe a curfew from 7pm to 7am and may be electronically tagged.
Solicitor John Wadham, the director of civil rights group Liberty, issued a lengthy statement on Mr Shayler's behalf.
"My conviction and imprisonment violated both my right to a fair trial and my right of freedom of expression and I intend to fight on," he said.
Mr Shayler will argue at the Court of Appeal that his convictions should be quashed because the trial procedure was "fundamentally flawed and unfair".
Liberty will argue Mr Shayler had to tell the prosecution about his cross-examination and defence in advance and he was unfairly excluded from secret hearings. The statement continued: "My conviction and sentence were also in breach of freedom of expression I was imprisoned for telling the truth about the incompetence and illegality in the Security Service.
"The government will have to justify the fact that it is a crime to report a crime when my case comes before the European Court of Human Rights."
The statement said Britain's ruling Labour Party would be challenged over its refusal to allow the public interest defence against charges of breaching Official Secrets Act.
Mr Shayler's girlfriend, former MI5 officer Annie Machon, said she was overjoyed her boyfriend was out in time for Christmas.
"It is far sooner than we could have ever dreamt of or hoped for," she said. "The brevity of the sentence reflects what he did.
"He has not been convicted of treason laws for which he would have got 14 years.
She added: "British people need to know what is going on in their name."
Mr Shayler revealed secret documents to the Mail on Sunday newspaper in 1997, arguing he had a public duty to expose malpractice within the security services.
The former MI5 officer was found guilty of disclosing information, documents and information from telephone taps in breach of the Official Secrets Act.
During the trial, the prosecution said he had potentially placed the lives of dozens of secret agents at risk.