The agitation of 1848 found M’Manus in good business as a shipping agent, his income being estimated by his Liverpool friends at ten or twelve hundred a year.  His patriotism was of too genuine a nature to be merged in his commercial success, and M’Manus readily abandoned his prospects and his position when his country seemed to require the sacrifice.  Instantly on discovering that the government were about to suspend the Habeas Corpus Act in Ireland, he took the steamer for Dublin, bringing with him the green and gold uniform which he owned in virtue of being a general of the ’82 Club.  In the same steamer came two detectives sent specially to secure his arrest in Dublin.  M’Manus drove from the quay, where he landed, to the Felon Office.  He discovered that all the Confederate leaders out of prison had gone southwards on hostile thoughts intent; and M’Manus resolved on joining them without a moment’s hesitation.  Having managed to give the detectives the slip, he journeyed southwards to Tipperary and joined O’Brien’s party at Killenaule.  He shared the fortunes of the insurgent leaders until the dispersion at Ballingarry, where he fought with conspicuous bravery and determination.  He was the first to arrive before the house in which the police took refuge, and the last to leave it.  The Rev. Mr. Fitzgerald, P.P., an eye witness, gives an interesting account of M’Manus’ conduct during the attack on the Widow M’Cormack’s house.  He says:—­

“With about a dozen men more determined than the rest, was M’Manus, who indeed throughout the whole day showed more courage and resolution than anyone else.  With a musket in his hand, and in the face of the enemy, he reconnoitered the place, and observed every accessible approach to the house, and with a few colliers, under cover of a cart-load of hay, which they pushed on before them, came up to the postern-door of the kitchen.  Here with his own hand he fired several pistol-shots, to make it ignite, but from the state of the weather, which was damp and heavy, and from the constant down-pour of rain on the previous day, this attempt proved quite unsuccessful.  With men so expert at the use of the pickaxe, and so large a supply of blasting powder at the collieries, he could have quickly undermined the house, or blown it up; but the circumstance of so many children being shut in with the police, and the certainty that, if they persevered, all would be involved in the same ruin, compelled him and his associates to desist from their purpose.”

When it became useless to offer further resistance, M’Manus retired with the peasantry to the hills, and dwelt with them for several days.  Having shaved off his whiskers, and made some other changes in his appearance, he succeeded in running the gauntlet though the host of spies and detectives on his trail, and he was actually on board a large vessel on the point of sailing for America from Cork harbour when arrested by the police.  His discovery was purely