Career
He boxed out of Massachusetts in the United States. His most notable bout was against Mike McCallum for the vacant WBA title, which he lost over a fifteen round unanimous decision. Newline Films reportedly plans to make a film about his life story.
In January 2014, Rocky Ros Muc: Seán Ó Mainnín, a biography about Mannion"s life and career was released.
The book is written in Irish but there are plans afoot to release an English version.
