Frank Lockyer said on Sunday he had gone through cycles of depression over Mrs Clark's life sentence in prison.
Speaking on the BBC's Breakfast with Frost, the 72-year-old said: "It was a rollercoaster as far as I am concerned."
Mrs Clark, from Cheshire, was released last week, after the Court of Appeal ruled her convictions were unsafe, following new medical evidence that was not presented at her trial.
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Sally herself probably had greater faith than I did that it had got to come right in the end
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Frank Lockyer, Sally Clark's father
Mr Lockyer said: "There were times when I had deep depression about it all, but at other times Sally herself probably had greater faith than I did that it had got to come right in the end.
"I am 72, you know you have got look at your life expectation now and if she was in prison for life imprisonment which could be anything up to 15 years."
Solicitor Mrs Clark from Wilmslow, was convicted and sentenced to life imprisonment more than three years ago of the murders of her two baby sons Christopher and Harry.
Close family friend John Batt said he felt the turning point in the case for her to be released came when Macclesfield Hospital handed over the medical notes of both babies.
'Immune deficiency'
He said: "In those medical notes was a microbiology report which showed that Harry definitely died of natural causes and overwhelming bacterial infection.
"It had never seen the light of day except to the original pathologist, it was never shown to other experts or the defence experts."
Mr Lockyer added that Sally's third son - now aged four - had suffered a similar condition to his elder brother Harry.
"This probably has great significance that there is a surviving child who also had an immune deficiency," he said.