O’Neill’s grandfather and father had both represented the family borough of Randalstown in the Irish Parliament, and the latter had subsequently sat for county Antrim before being raised to the peerage as Baron (1793) and Viscount O’Neill (1795). Killed during the Rebellion in 1798, he was succeeded by O’Neill’s elder brother Charles Henry St. John, who was given an Irish earldom at the time of the Union, became a representative peer in 1801 and was grand master of the Orange Order. It was on his interest that O’Neill had sat for Antrim since 1802.
O’Neill sided with opposition for information on the plot to murder the Irish lord lieutenant, 24 Mar. 1823, and was apparently ready to resign his place in order to vote for Brownlow’s intended motion on the use of ex-officio informations against the Orangemen implicated in the affair.
serious representation made or to be made to Lord Liverpool by some of the Irish Members against the system of reform now happily proceeding in this country on the ground of its interfering with the patronage, the continuance of which in its full extent was a condition of their support in carrying the Union and threatening that if it is persisted in they will withdraw their assistance from government ... I am told too it is to be presented by Col. O’Neill ... Lord L. will know how to deal with it and with pretensions of such incomparable absurdity.
Add. 57401, f. 149.
He divided for the Irish unlawful societies bill, 25 Feb., and against Catholic relief, 1 Mar., 21 Apr., 10 May, and the Irish franchise bill, 26 Apr. 1825. He was promoted major-general in May, but in October 1825 ministers declined to promise a peerage to Lord O’Neill with a special remainder to him.
He attended an Antrim county meeting to agree an address of condolence on the death of the duke of York, 6 Feb. 1827, and that month signed the Irish Protestants’ anti-Catholic petition. Bringing up the county’s anti-Catholic petition, 2 Mar., his colleague MacNaghten stated that he was absent through illness but supported its plea.
O’Neill was granted one month’s sick leave, 5 Mar. 1830, and must have missed most or all of that session. He offered again at the dissolution in July, when his brother’s adroit switch of allegiance from Lord Hertford to Lord Donegall was considered enough to ensure his return with the latter’s son, Lord Belfast.
Aware of the need to maintain popularity in Belfast, he came round to supporting parliamentary reform and promised to support the Belfast and county petitions in its favour.
That month, when he applied to ministers for a military or colonial position, the duke of Richmond commented that ‘he is a real Irishman and expects a reward’ and that Lord O’Neill ‘only supported the government to secure either a peerage or employment for his brother’; nothing came of it.
