[F]rom the history of the early periods of this corporation, and a view of its charters and bye-laws, it appears that the Commons had, from the earliest periods, participated in the important right of election to that high trust ; and it was natural and just that the whole body of citizens, by themselves or their representatives, should have a share in electing those magistrates who were to govern them, as it was their birthright to be ruled only by laws which they had a share in enacting. The Aldermen, however, soon became jealous of this participation, encroached by degrees upon the Commons, and at length succeeded in engrossing to themselves the double privilege of eligibility and of election; of being the only body out of which, and by which the Lord Mayor could be chosen.
Nor is it strange that, in those times, a board consisting of so small a number as twenty-four members, with the advantages of a more united interest, and a longer continuance in office, should have prevailed, even contrary to so evident principles of natural justice and constitutional right, against the unsteady resistance of competitors so much less vigilant, so much more numerous, and, therefore, so much less united. It is the common fate of the indolent to see their rights become a prey to the active. The condition upon which God hath given liberty to man is eternal vigilance, which condition if he break, servitude is at once the consequence of his crime, and the punishment of his guilt.
“Election of Lord Mayor of Dublin,” speech before the Privy Council, July 10, 1790.
From Thomas Davis (ed) (1847) The Speeches of the Right Honorable John Philpot Curran, pp. 103-131 (archive.org). Quote is from p. 105.
John Philpott Curran was one of the best-known lawyers of his time. He had associations with the United Irishmen and defended Archibald Rowan Hamilton. The above quote is from one of his political speeches made on the occasion of a disputed election. The agreement of both Aldermen and the Common Council was required to elect a Lord Mayor but the aldermen disputed the validity of the Common Council’s rejection of their selection. Curran’s famous linking of liberty and vigilance was made while reviewing the background to the dispute as the extended quote above makes clear.
The last two sentences are the ones most commonly quoted and Bartlett’s Familiar Quotations (1980, 15th ed, p. 397, footnote 8) gives them as the source of “eternal vigilance is the price of liberty” .