One of his first public acts was to join Sir Warham St. Leger in trying and executing at Cork in August, 1580, Sir James Fitzgerald, the Earl of Desmond's brother. Fitzgerald was drawn, hanged, and quartered. His immediate superior was the Earl of Ormond, the Lieutenant of Munster, who showed occasional tenderness to his fellow-countrymen. The Lord Deputy was Lord Grey of Wilton, whose views were generally as stern as Ralegh's. Edmund Spenser was assistant secretary to Grey, and held as austere a theory of Irish government. Ralegh in November, 1580, was with Lord Grey's army. With the assistance of an English fleet under Admiral Winter it blockaded at Smerwick in Kerry a mixed Spanish and Irish garrison. On November 10 the garrison capitulated without conditions. Thereupon Grey sent in Ralegh and Macworth, who had the ward of the day. They are stated by Hooker, in his continuation of Holinshed, to have made a great slaughter. Four hundred Spaniards and Italians were put to the sword. All the Irishmen and several Irish women were hanged. An Englishman and an Irish priest, who suffered the same doom, had their legs and arms first broken. Only the foreign officers were held to ransom. The act was that of the Deputy. Afterwards it was discovered that the massacre excited general horror through Europe. Attempts were made to repudiate sympathy with it on the Queen's part. Bacon wrote that she was much displeased at the slaughter. Her own letters to Grey comment on the whole proceeding as greatly to her liking. She expresses discontent only that she had not been left free to kill or spare the officers at her discretion. Personally Ralegh cannot be accounted amenable for the atrocity. He is not named in Grey's despatch to the Council. But it would be folly to pretend that he disapproved it. Hooker, his eulogist, claims it for him as an eminent distinction. He cordially sympathized with Grey's ideal of a Mahometan conquest for Ireland.
His Irish service gave him opportunities of a nobler order. He ventured his life in a score of hazardous feats. On one occasion his horse was desperately wounded. He must have been slain but for the aid of his servant Nicholas Wright, a trusty Yorkshireman. Another time the Seneschal of Imokelly with fifteen horsemen and sixty foot lay in wait for him at a ford between Youghal and Cork. He had crossed in safety when Henry Moile, one of a few Downshire horsemen he had added to his foot soldiers, was thrown in the middle of the stream. Back rode Ralegh, and stood by his comrade in the face of tremendous odds. The Seneschal, though his men outnumbered Ralegh's by twenty to one, was intimidated. He let Ralegh accomplish his purpose, which was the occupation of Barry's Court, the seat of Lord Barry. Barry was one of the Irish nobles whose loyalty was not fixed. Ralegh desired to convince the class of the futility of resistance by sudden blows. His courage in this instance was more apparent than his wisdom. He had with difficulty obtained the Deputy's consent to the enterprise. The result justified Grey's hesitation. Barry had escaped before Ralegh's arrival at his castle. He became, and remained for years, an open enemy. At last he seems to have been reconciled to the Government. In 1594 Ralegh was interceding for him against the grant of a favour at his expense to another veteran malcontent, Florence MacCarthy. Ralegh's vigour had fuller success against another suspected noble, Lord Roche, of Bally. Roche's castle, twenty miles from Cork, was strong, and his retainers devoted and many. With a petty detachment Ralegh set off on a dark night. He foiled two bands, one of eight hundred, the other of five hundred, which endeavoured to block his way. During a parley he contrived to introduce first a few and then all his followers. Lord Roche professed much loyalty, and entertained the intruders courteously at dinner. He refused to accompany Ralegh on his return till he was shown that the castle was in the hands of the English soldiers. Reluctantly he yielded, and Ralegh conveyed him and his family across the rugged hills into Cork by night. Roche proved an excellent subject.