Mr Bain, who married Christchurch primary school teacher Liz Davies in January, has confirmed the arrival of their son.
He contacted the Otago Daily Times yesterday to read the following statement: ''Elizabeth and I are delighted to announce the arrival of our beautiful son. We are all delighted, happy, and in good health.''
The baby is understood to have arrived on Wednesday.
The couple, who live in Christchurch, met a decade ago. In July, they confirmed they were expecting a baby.
Long-time supporter Joe Karam said the birth was ''a very satisfying reward'' given his efforts over the past 20 years.
''I am delighted for David and Liz.''
Mr Bain was convicted in 1995 of murdering his parents, two sisters and brother in their Every St home, and spent 13 years in jail before he was acquitted in a 2009 retrial in Christchurch.
Mr Bain's compensation claim was put on hold by the Cabinet in January 2013, at Mr Bain's request, pending the completion of judicial review proceedings.
