He was educated at Mount St Benedict's, in Gorey, County Wexford, University College Dublin and King's Inns.

After some time at Marshall Field's in Chicago he returned to Ireland where he became manager of the family business known as Monica Duff's in Ballaghaderreen, County Roscommon.

Dillon resigned from Fine Gael in 1942 over its stance on Irish neutrality during World War II.

His zeal against Hitler drew him the ire of the German Minister to Ireland Eduard Hempel, who denounced him as a "Jew" and "German-hater".

[6][7] In 1944, as the danger of allied defeat receded he was approached by Fine Gael to rejoin the party and offered the leadership, on condition he relinquished his views on neutrality, especially since they were no longer strategically important.

[2] Dillon was one of the independents TD who was part of the first inter-party government (1948–1951), and was appointed Minister for Agriculture.

On Northern Ireland, while Dillon stood against Partition, he equally opposed any "armed solution" or militant nationalist policy, stating: We have got to win, not only the barren acres of Ulster, but the hearts of the people who live in it[5]Dillon was a colourful contributor to Dáil proceedings and was noted for his high standard of oratory.