King’s father, an army officer who once fought an inconsequential duel with his sister’s disreputable lover, was the second son of the 2nd earl of Kingston, on whose death in 1799 he inherited the heavily indebted but subsequently much improved Rockingham estate in Roscommon.
However, he certainly voted against Catholic relief, 6 Mar. 1827, when his cousin and uncle were listed in the favourable minority. Opposition votes by the ‘Hon. R. King’ in that and later sessions were probably given by Robert Henry King; unless it was he who spoke for going into committee on the corn bill, 25 Apr. 1828, he was apparently silent in debate, as the presentation of numerous petitions in this Parliament can safely be attributed to the Member for county Cork. He missed the division on Catholic relief, 12 May, yet in reply to a letter from the O’Conor Don, the leading local Catholic, which was aired at a dinner in December 1828, he apparently revealed that he would now vote in its favour.
By the mid-1830s, when he suffered a stroke, King had started to feel the physical effects of his heavy drinking and by the 1840s he had debts of at least £40,000. He was almost entirely under the influence of his wife, the high living daughter of an Irish baronet, who was strongly disapproved of by her father-in-law. In 1840 Lorton managed to settle them into a more sober and regular lifestyle at Frankfurt, but from 1846 she contracted a relationship with a dubious and insolvent French nobleman, Vicomte Ernest Valentin de Satgé St. Jean. When she bore a son, Henry Ernest Newcomen, in 1848, King disowned the child, but continued to live with his wife and her lover despite pressure from his father; when he did sue for divorce in 1850 the legal proceedings failed because he was found to have committed adultery with his nursemaid and travelling companion, Julie Imhoff, who later lived openly with him as his mistress. In desperation, Lorton, who feared that his elder son and elder grandson’s inheritance would be wrested from them, succeeded in gaining custody of his two grandchildren, Frances and Robert Edward, and, by various codicils to his will, left the unentailed parts of his estates to his second son Lawrence Harman King Harman of New Castle, county Longford. On succeeding to the viscountcy in 1854, King put Rockingham in trust for his acknowledged son and for many years lived quietly in London. However, his estranged wife was unceasing in her efforts to advance the interests of her second son, and he and his Kingston cousins were driven to extraordinary lengths to exclude ‘the Frenchman’, as they called him, from inheriting their patrimony. As a result, after the deaths of this Member, who had become the 6th earl of Kingston, in 1869 and Robert Edward, the 7th earl, in 1871, the peerage but not the hereditary lands, which were disastrously dispersed, passed to Henry Ernest Newcomen King Tenison, whose legitimacy was confirmed (as it could not be disproved) at the probate court in Dublin in 1870.