He laboured and wrote to secure Catholic emancipation, legislative independence, justice for tenants and the poor, and vigorously assailed the proselytizers and the government's proposal for a mix-faith national school system.

[6][7] Three important events happened during John's childhood: the Irish Rebellion of 1798; the landing at Killala of French troops, whom the boy, hidden in a stacked sheaf of flax, watched marching through a mountain pass to Castlebar; and a few months later the execution of Father Conroy on a charge of high treason.

[9] About this period he commenced a series of letters to the Dublin Journal, signed "Hierophilus", vigorously attacking the Irish Established Church's system of religious education in schools.

[10] MacHale attended the annual meeting of the Irish bishops, and gave evidence at Maynooth College before the Parliamentary Commissioners then inquiring into the condition of education in Ireland.

After witnessing the coronation of William IV at Westminster Abbey, the bishop, requiring change of air on account of ill-health, went on to Rome, but not before he had addressed to the premier another letter informing him that the scarcity in Ireland "was a famine in the midst of plenty, the oats being exported to pay rents, tithes, etc., and that the English people were actually sending back in charity what had originally grown on Irish soil plus freightage and insurance".

On the other hand he severely condemned the Government for its incapacity, its indifference to the wrongs of Ireland, that aroused in the Irish peasantry a sullen hatred unknown to their more simple-minded forefathers.

Amid the varied interests of the Eternal City he was ever mindful of Ireland's woes and forwarded thence another protest to Earl Gray against tithes, and proselytism, this last grievance being then rampant, particularly in Western Connacht.

On his return he became an opponent of the proposed system of non-sectarian 'National Schools', fearing that the bill as originally framed, was an insidious attempt to weaken the faith of Catholic children.

Oliver Kelly, Archbishop of Tuam, died in 1834, and the clergy selected MacHale as one of three candidates, to the annoyance of the Government who despatched agents to induce the pope not to nominate him to the vacant see.

MacHale also led the opposition to the Protestant Second Reformation, which was being pursued by evangelical clergy in the Church of Ireland, including the Bishop of Tuam, Thomas Plunket.

He founded his own schools, entrusting those for boys to the Christian Brothers and Franciscan friars, while Sisters of Mercy and Presentation Nuns taught the girls.

The repeal of the Union, advocated by Daniel O'Connell, enlisted his ardent sympathy and he assisted the Liberator in many ways, and remitted subscriptions from his priests for this purpose.

His biographer Bernard O'Reilly describes MacHale as supporting "a thorough and universal organisation of Irishmen in a movement for obtaining by legal and peaceful agitation the restoration of Ireland's legislative independence".

In this he differed considerably from some other Irish prelates, who thought that each bishop should exercise his own judgment as to his acceptance of a commissionership on the Board, or as regarded the partial application of the Act.

In his zeal for the cause of the Catholic religion and of Ireland, so long down-trodden, but not in the 1830s, Dr. MacHale frequently incurred from his opponents the charge of intemperate language, something not altogether undeserved.

Then by 1846 he warned the Government as to the state of Ireland, reproached them for their dilatoriness, and held up the uselessness of relief works expended on high roads instead of on quays and piers to develop the sea fisheries.

At a conference held in Dublin, there was cross-denominational support for his views on "fixity of tenure, free sale, and fair rent", and these were provided for in the Landlord and Tenant (Ireland) Act 1870.

[18] In 1877, to the disappointment of the archbishop, who desired that his nephew should be his coadjutor, John McEvilly, Bishop of Galway, was elected by the clergy of the archdiocese, and was commanded by Pope Leo XIII after some delay, to assume his post.

[citation needed] Every Sunday he preached a sermon in Irish at the cathedral, and during his diocesan visitations he always addressed the people in their native tongue, which was still largely used in his diocese.

The Cork-born Irish-American composer Paul McSwiney (1856–1890) was in the process of writing the cantata John McHale for centenary celebrations in New York City in 1891, but died before he could complete it.