He accompanied Sir Henry Sidney into Connacht in September 1576, and having been knighted by him on 7 October, was appointed colonel, or military governor, of the province (called
Connaught by the English). Malby then proceeded against John and Ulick Burke, sons of the
Earl of Clanricarde, harrying their countries with fire and sword. In October 1577, after arranging a feud between
O'Conor Don and MacDonough, he, at
O Connor Sligo's request, attacked the castle of
Bundrowes, and having captured it from O'Donnell, restored it to O'Conor Sligo. But not having much confidence in the loyalty of the latter, he appointed Richard MacSwine
High Sheriff of Sligo. Shortly afterwards O'Donnell invaded the county, slew the sheriff, and besieged Bundrowes, compelling him to retrace his steps. He drove O'Donnell out of the county, but was unable to overtake him. At Sligo, on his way back to
Roscommon, he came to terms with
Brian O'Rourke, but the arrangement did not last long, owing to O'Rourke's refusal to expel certain coiners he maintained. In April 1578 Malby invaded his country, captured his chief castle, and put the entire garrison to the sword. In the autumn of 1578 he went to England, returning to Ireland in May 1579, with the higher title of president of Connaught. After the failure of Essex's colonisation project, his grant of MacCartan's country had been, by Sidney's advice, revoked; but he, on 12 April 1579, received a grant of the manor and lordship of Roscommon, together with an annual rent of 200
l. out of the composition paid by the O'Farrells, and certain lands in
Longford. During his absence in England his officers and soldiers behaved badly, but Connacht remained tranquil; on the outbreak of
James Fitzmaurice's
Second Desmond Rebellion in July, Malby, with six hundred troops, marched to
Limerick to co-operate with the lord justice,
Sir William Drury. Owing to Drury's illness the task of suppressing the rebellion devolved mainly upon him. On 3 October he defeated Sir John and Sir James of Desmond at
Monasteranenagh in county Limerick. He strongly suspected the Earl of Desmond of disloyalty, and after several ineffectual efforts to secure his co-operation, treated him as a rebel; while Desmond complained that Malby's severity was a chief cause of his rebellion. On the arrival of the
Earl of Ormonde in November with a commission to command the army in Munster, Malby returned to his charge in Connacht. He belonged to the Leicester faction, and for this and other more personal reasons bore no goodwill to Ormonde, whom he subsequently charged with misrepresenting his services in Munster, and with abetting disorder in Connacht. With the exception of Richard Burke, called Richard of the Iron, or Iron Dick, none of the Connacht chiefs had shown any active sympathy with the Munster rebels. In February 1580 Malby invaded his country and drove him to seek safety among the islands in
Clew Bay. After suffering the most terrible privations, Richard of the Iron submitted to the garrison at
Burrishoole. During the
siege of Carrigafoyle, Malby assisted the operations of the lord justice,
Sir William Pelham, with supplies from Connacht. In August O'Rourke, expecting foreign assistance, rebelled and dismantled the castle of
Leitrim. Malby immediately took the field against him, repaired and garrisoned the castle, and routed the rebels. Then, hastening to Dublin to the assistance of the lord deputy,
Arthur, Lord Grey of Wilton, against
Baltinglas and
Fiach McHugh O'Byrne, he witnessed the defeat of the English forces at
battle of Glenmalure. O'Rourke was again in arms and Malby returned to Connacht. O'Rourke fled at his approach; but John and Ulick Burke, at the instigation of the catholic
bishop of Kilmacduagh, had proclaimed a religious war, and were making efforts to relieve the Spanish at
Smerwick. Even after the capture of Smerwick Grey sent reinforcements, but by the end of January 1581 Malby announced success against the rebels. O'Rourke took advantage of the situation, and invaded Roscommon, but Malby sent Captain Brabazon against him, and O'Rourke then sued for peace. Towards the end of February a body of six hundred Scots invaded the province to co-operate with the Burkes, but Malby had notice of their arrival, and drove them across the
Moy River. At
Strade Abbey, in
County Mayo, he decided a controversy between Richard of the Iron Burke and Richard MacOliver, allowing the title of MacWilliam to the former, and making the latter sheriff of the county of Mayo. In May he agreed to a short peace with the Burkes, intending to visit court, but on the outbreak of hostilities between
Turlough Luineach O'Neill and
Hugh O'Donnell in July, he was ordered to the assistance of O'Donnell. He marched as far as
Lifford, and having destroyed the town, effected a junction with the lord deputy. Towards the close of November he went to England to report on the general situation of affairs in Ireland. But, so far as he was personally concerned, his visit was not successful. Enemies charged him with violent, tyrannical, and corrupt conduct in his administration, and Elizabeth showed a disposition to listen to the charge. He returned to Ireland on 21 May 1582, where early in July,
Con O'Donnell, at the instigation of Turlough Luineach, invaded
Sligo. Malby complained that the order forbidding him to raise men by cessing them on the country rendered him powerless to meet this danger. But O'Conor Sligo behaved well, and at Malby's approach O'Donnell quickly crossed the
Erne River. After this nothing occurred during his lifetime to disturb the peace of his government. On 4 March 1584 he died at
Athlone, feeling ingratitude on the part of the Queen. "He was a man learned in the languages and tongues of the islands of the west of Europe, a brave and victorious man in battles", according to the
Annals of the Four Masters, s.a. 1584. ==Family==