Little is known of Mackillop’s family background, other than that his parents were married at Kilmadock in 1781.
The Wellington ministry listed Mackillop as one of their ‘friends’, and he voted with them in the crucial division on the civil list, 15 Nov. 1830. He divided against the second reading of the Grey ministry’s reform bill, which proposed to disfranchise Tregony, 22 Mar., and for Gascoyne’s wrecking amendment, 19 Apr. 1831. At the ensuing general election he was again returned for Tregony, after a contest. He divided against the second reading of the reintroduced reform bill, 6 July. He voted for use of the 1831 census in determining the disfranchisement schedules, 19 July, against the inclusion of Chippenham in schedule B, 27 July, and making proven payment of rent a prerequisite for voting, 25 Aug., and to preserve the freeholder franchise of the four sluiced boroughs, 2 Sept. He divided against the bill’s passage, 21 Sept. He voted for inquiry into the state of the West India interest, 12 Sept. He divided against the second reading of the revised reform bill, 17 Dec. 1831, going into committee, 20 Jan., the enfranchisement of Tower Hamlets, 28 Feb., and the third reading, 22 Mar. 1832. He voted for inquiry into the glove trade, 3 Apr., and an Irish absentee tax, 19 June. He divided against government on the Russian-Dutch loan, 12 July 1832. He is not known to have spoken in debate. Having been a member of the committee appointed by the London East India merchants in 1830 to consider the impending renewal of the Company’s charter, he had returned written answers to questions on Indian trade from the board of control the following year, and was added to the select committee on the Company’s affairs, 22 Feb. 1832.
At the general election of 1832 Mackillop made a late entry into the field at Southampton, where another Conservative was challenging two reformers. He stressed his credentials as a commercial man, whose expertise would enable him to ‘fill your port with shipping, and your town with trade’. He claimed that he ‘belonged to no political party’ and ‘had always been independent’, but promised to ‘oppose rash innovations’ and support ‘the most rigid economy’ and the elimination of abuses. He finished a very distant fourth.
