Professor Shannon is deputy director of Education at the Law Society of Ireland. He is a leading authority in Child Law and Family Law. He has held a variety of roles including chairman of the Adoption Board and its successor the Adoption Authority of Ireland (AAI).

In 2006 he was appointed as the special rapporteur on Child Protection. He has been re-appointed by successive governments to this role as an independent legal expert. In 2010, he was appointed by the government to chair and co-write the Independent Child Death Review.

The Independent Child Death Review Group (ICDRG) examined the deaths of 196 children who died in state care between 2000 and 2010. He has also been involved in judicial training on all aspects of international family and child law. He is a senior lecturer in Child and Family Law at the Law Society of Ireland.

He has written or co-written 30 books, 36 articles in refereed journals, and 42 articles in professional magazines on the area of child law and family law. He was awarded the LLD by UCD on the basis of his published work.