Dillon was appointed a Fenian leader in Cork by James Stephens, the head of the Irish Republican Brotherhood.

[1] In September 1865, police arrested Fenian leaders James Stephens and O'Donovan Rossa in Dublin, and Brian Dillon in Cork.

The police searched Dillon's home and found a pair of field glasses, some drawings, and some incriminating letters sewn into the mattress of his bed.

[5] Both were found guilty, based primarily on the testimony of informants [6] although John Warner's account was very weak and unsatisfactory under cross examination.

In January 1866 Dillon and John Sarsfield Casey (the Galtee Boy) were handcuffed together on the tough and rough sea crossing between Kingstown and Holyhead.

The train reached Cork at 8:00 p.m. and even though a carriage and pair were waiting, he was glad to seek refuge in the first covered car he could find, so dense was the crowd all around him, willing to shake his hand.

The triumphal procession from the station to his home then began, and the hills all along the route were lighted with tar barrels.

[2] Amid emotional scenes Brian Dillon met his family, and afterwards appeared at one of the windows of the house and thanked the people of Ireland for the great reception he had received everywhere on his journey home to Cork.

On Monday 18 August, his remains were privately borne to St. Joseph's cemetery, to a temporary resting place, as it was decided to build a vault in the family burial ground in Rathcooney, and this would not be ready for a few days.

On arrival at the newly built tomb, so dense was the crowd that milled around the hearse, that considerable difficulty was experienced in getting the coffin to the grave.

Then the priests read the burial service, and in a hushed silence, Canon Freeman asked the entire assembly to kneel and recite the Lord's Prayer aloud.