He left school at 13 to work as delivery boy for White Heather Laundry, learning Dublin neighbourhoods with great thoroughness.

[2] Mac Thomáis joined the Dublin Brigade of the Irish Republican Army as a young man and was active in the preparations for and prosecution of the 1956-62 border campaign.

He was interned in Curragh Camp during the campaign and in December 1961 was sentenced to 4 months imprisonment under the Offences Against the State Act.

Editors of six left-wing and Irish-language journals called for his release, as did a number of writers, and hundreds attended protest meetings - to no avail.

[3] Tim Pat Coogan, editor of the Irish Press, claimed the charges against Mac Thomáis were politically motivated to a large degree as his activities were confined strictly to the newspaper An Phoblacht.

[6] Under Section 31 of the Broadcasting Act, due to his membership of Sinn Féin in the 1970s he was removed from his position in making some of the RTÉ historical programmes.