Landing at Killala

In 1798, the Irish Rebellion of 1798 against British rule in Ireland broke out. Teeling returned to Ireland on 22 August 1798, as an aide-de-camp to General Jean Humbert, and landed at Killala Bay between County Sligo and Mayo with a force of French troops. On 28 August, Humbert's men captured Castlebar and the United Irishmen subsequently established the Republic of Connacht. Humbert's troops, having combined forces with local rebels, pushed east through County Sligo but were halted by a cannon which government forces had installed above Union Rock near Collooney.^{[citation needed]}

Battle of Collooney

On 5 September 1798, Teeling participated in the Battle of Collooney. He cleared the way for a Franco-Irish victory by single-handedly disabling the cannon installed at Union Rock during the battle after breaking from the French ranks and galloping towards the enemy armed with a pistol. Teeling killed the gunner manning the cannon and captured it, allowing the combined Franco-Irish force to advance and forcing their opponents to retreat towards their barracks in Sligo, having suffered 60 men killed and 100 captured.^[3][4]

Battle of Ballinamuck and execution

During the Battle of Ballinamuck, which was fought near Longford, Teeling and approximately 500 other Irishmen were captured along with their French allies. The French were treated by the Dublin Castle administration as prisoners of war and were eventually returned to France, but the Irish prisoners were executed. Teeling was court-martialled after his capture. To positively identify him, the authorities enlisted William Coulson, a damask manufacturer from Lisburn, who identified him as a son of Luke Teeling, a linen merchant who lived in Chapel Hill, Lisburn. Teeling was hanged at Arbour Hill Prison in Dublin.^[5][6]

Teeling attempted to read the following statement from the scaffold, but was not permitted to:

Fellow-citizens, I have been condemned by a military tribunal to suffer what they call an ignominious death, but what appears, from the number of its illustrious victims, to be glorious in the highest degree. It is not in the power of men to abase virtue nor the man who dies for it. His death must be glorious in the field of battle or on the scaffold.

The same Tribunal which has condemned me —Citizens, I do not speak to you here of the constitutional right of such a Tribunal, —has stamped me a traitor. If to have been active in endeavouring to put a stop to the blood-thirsty policy of an oppressive Government has been treason, I am guilty. If to have endeavoured to give my native country a place among the nations of the earth was treason, then I am guilty indeed. If to have been active in endeavouring to remove the fangs of oppression from the head of the devoted Irish peasant was treason, I am guilty.

Finally, if to have striven to make my fellow-men love each other was guilt, then I am guilty. You, my countrymen, may perhaps one day be able to tell whether these were the acts of a traitor or deserved death. My own heart tells me they were not and, conscious of my innocence, I would not change my present situation for that of the highest of my enemies.

Fellow-citizens, I leave you with the heartfelt satisfaction of having kept my oath as a United Irishman, and also with the glorious prospect of the success of the cause in which we have been engaged. Persevere, my beloved countrymen. Your cause is the cause of Truth. It must and will ultimately triumph.^[7]

He is believed to have been buried at the mass grave of rebels at Croppies' Acre, Dublin.