Henaghan attended school in Timaru and studied law at Otago University.
On qualifying he became a teaching fellow, providing advice, helping with submissions, and training Family Court judges.
[2] Henaghan is the second academic to be admitted as an Associate Fellow of the International Academy of Matrimonial Lawyers (IAML).
The academy is a worldwide association of practising lawyers who were recognised by their peers as being among the most experienced and skilled family law specialists in their respective countries.
He enjoys attending afternoon movie sessions and once had a cameo role in the New Zealand film Scarfies, as himself.