Professor Sir Roy Meadow has won his High Court appeal against the General Medical Council's decision to strike him off the medical register.
Sir Roy denied serious professional misconduct
The judge also overturned the GMC's ruling that the paediatrician was guilty of serious professional misconduct.
The case against him centred on his testimony at the 1999 trial of Sally Clark for the murder of her babies.
She won her appeal against her imprisonment in 2003.
During Mrs Clark's trial, Sir Roy said the probability of two natural unexplained cot deaths in the family was 73 million to one.
The figure was later disputed by the Royal Statistical Society and other experts said that once genetic and environmental factors were taken into consideration, the odds of a second cot death in the same family were closer to 200 to one.
Sir Roy also gave evidence as an expert witness in the trials of two other women, Angela Cannings and Donna Anthony, who were both freed on appeal after being convicted of murdering their children.
He retired from clinical practice in 1998, but wanted to restore his reputation with this appeal.
But the GMC has expressed concern, saying the verdict raised questions over whether doctors were immune from its investigations.
In a statement released after the verdict, Sir Roy said: "I am relieved that the court has quashed the GMC's decision.
"Children can only be protected from abuse if those who suspect abuse are able to give their honest opinion without fear of retribution.
Sally Clark: Served three years after being wrongly convicted of killing her two sons
Angela Cannings: Served 18 months after being wrongly convicted of killing her two sons
Donna Anthony: Served six years after being wrongly convicted of killing her son and daughter
Trupti Patel:Acquitted of killing three of her children
"This is an important decision for paediatricians and all doctors, nurses, teachers and other professionals who may have to express difficult and sometimes unpopular opinions in the course of giving evidence in court.
"They should be able to do so without the fear of prosecution by the GMC or other professional regulators."
But Angela Cannings said she was "disappointed and disheartened" by the decision.
High Court judge Mr Justice Collins explained his decision to overturn the GMC's verdicts by saying: "It is very difficult to think that the giving of honest, albeit mistaken evidence could - save in an exceptional case - properly lead to such a finding."
The judge also ruled Sir Roy's actions could not "properly be regarded" as serious professional misconduct.
In a statement, the GMC said it did not want its work to inhibit doctors from acting as expert witnesses.
But it added: "Where there has been serious judicial criticism, we have sought to act to protect the public interest from experts who fall significantly short of accepted standards."
The GMC had said evidence given by Sir Roy in Mrs Clark's case had been misleading, although she was actually freed after it became apparent that another witness at her trial, pathologist Alan Williams, had failed to disclose key medical evidence.
John Batt, a friend of the Clark family, expressed concern over the High Court verdict.
"It's not right that the professional bodies should be neutered because of an immunity of their members for anything that is said in court."
Sanction was 'too draconian'
Dr Christine Tomkins, deputy chief executive of the Medical Defence Union, which has supported Sir Roy, said: "The MDU has been defending doctors for over 120 years and seldom have we come across a judgment that we consider to be as unfair and disproportionate as the GMC's erasure of Professor Meadow from the medical register.
She added: "It is in the public interest that doctors should be able to provide expert opinion in cases where there are allegations of child abuse without fear that they will be the subject of a finding of serious professional misconduct for expressing a genuinely held belief."
Tom Magner, of the Society of Expert Witnesses added: "This verdict gives a heart-warming message to expert witnesses that they need not fear vexatious complaints."
Professor Sir Alan Craft, President of the Royal College of Paediatrics and Child Health, said: "This is a welcome result for Professor Meadow, the RCPCH and every paediatrician and doctors in general.
"If the original decision had stood there is a real danger that doctors across all specialities would have become reluctant to undertake vital expert witness work."