In January 1848,
John Mitchel visited Cork and, according to Michael Cavanagh, who would publish a sketch of his Brenan's life in
Young Ireland, Dublin, in June and July 1885, Brenan for the first time "beheld the man he most admired on earth, and with whose future destiny, whether for weal or woe, he felt his own was bound up. Never had the arch-enemy of England a more faithful or earnest follower." Brenan contributed to the Mitchel's
United Irishman and, sold his rifle to obtain his train fare, to take up his residence in
Dublin, the headquarters of the revolutionary movement. He later published articles in
John Martin's
Irish Felon urging the Confederate Clubs members, many of whom had arms to be in readiness for action. "The sooner you realise the fact," he wrote in a
Letter addressed to the Members of the Provincial Confederate Clubs, "that the Confederation was got up for the purpose of doing something, the better for us all. Just think what it undertook to do. It undertook to defeat the strongest Government and to liberate the most degraded country that ever existed. It undertook to give – to a province—to strike the chains off millions of slaves and, if necessary, to wash out the, iron moulds in blood." In another Letter to "
the Young Men of Ireland" on 22 July 1848, he wrote: "On you I principally rely. You realise that you are very 'rash,' rather inclined to be 'violent,' and have exceedingly little prudence to spare. Brothers, let your watchword be 'Now or never—now and for ever' rashly" Brenan was associated with
John Savage and
John O'Mahony while Savage was operating on the slopes of the
Comeragh Mountains. Brenan was arrested and kept in prison for seven months alternately in Newgate Prison, Carrickfergus and
Kilmainham Gaols. During his confinement he wrote some fine poems, according to T. F. O'Sullivan, one, entitled "
Yearnings," evidently addressed to Mary Savage, sister of John. After his release without trial in March 1849, Brenan became editor of the
Irishman which had been started in Dublin by Bernard Fulham, and for six months attempted to rekindle the insurrectionary flame in the country. He was implicated in the attack on the
Cappoquin police barracks on 16 September 1848 and in October escaped to America. ==Escape to America==