O'Shea, William Henry (1840–1905), politician and adventurer, was born in Dublin, son of Henry O'Shea (pronounced ‘O'Shee’), a catholic solicitor from an indebted Limerick gentry family, and his wife Catherine, a papal countess and daughter of Edward Craneach Quinlan of Rosana, Co. Tipperary. He had one sister, Mary, who spent many years with her mother in Paris. William was educated at St Mary's College, Oscott, near Birmingham, and spent a term at the new Catholic University in Dublin, where the rector, John Henry Newman (qv), regarded him as sufficiently disruptive to expel him. Although he was briefly enrolled at TCD, his father purchased him a commission in the 18th Hussars (1858), where O'Shea lived extravagantly, largely at his family's expense. As a captain, he sold his commission in 1862 to clear his debts and entered a partnership with his uncle, owner of a bank in Madrid. On 24 January 1867, in Brighton, Sussex, after a lengthy courtship, he married Katharine Wood of Bradwell, Essex, youngest daughter of the Rev. Sir John Page Wood, anglican clergyman, and his wife, Emma Caroline (née Michell).
After living briefly with Katharine in Madrid, he acrimoniously severed his banking partnership and the O'Sheas relocated to England, where William tried unsuccessfully to establish a stud farm at Bennington, Hertfordshire. He returned to Spain to manage a mine, which also failed. His marriage became one of convenience, although the couple had three children: a son, Gerard (b. 1870), and two daughters, Norah (b. 1873) and Carmen (b. 1874). William lived mainly in London while Katharine and the children settled (1875) at Eltham, Kent, near her generous but demanding widowed aunt, Mrs Maria Wood (‘Aunt Ben’). Since Katharine's father's death (1866) Aunt Ben had financially supported her and, by extension, Capt. O'Shea. He benefited sufficiently to endure an empty marriage in the hope of future good fortune through Mrs Wood's will. Although living apart (she at successive addresses in Brighton), he and Katharine appeared together in public to support his political aspirations.
Encouraged by Liberal friends in Ireland, O'Shea was elected home rule MP for Co. Clare (April 1880). At heart he remained a Liberal (or ‘whig’, to his detractors in the Irish party, which had an uneasy working relationship with the Liberals). He was distrusted by his colleagues and weak in political acumen; his most positive achievement was to begin negotiations leading to the ‘Kilmainham treaty’ of May 1882, whereby his leader and increasingly personal rival, Charles Stewart Parnell (qv), abandoned militant land war politics for constitutional cooperation with the Liberal administration of W. E. Gladstone. In the summer of 1880 O'Shea and his wife had met Parnell, who quickly began an affair with Katharine. Soon becoming angrily aware of the situation, O'Shea accommodated it to preserve his political and financial interests, even when his wife had become Parnell's mistress and had had three children outside the marriage by 1884. His half-hearted attempts to renegotiate the failing home rule–Liberal ‘treaty’ for Parnell in 1884–5 were unsuccessful. He himself faced the embarrassment of a no-confidence motion by the National League in Co. Clare in June 1884. Steadily, relations with party colleagues, in whom he showed little interest, deteriorated.
O'Shea's political career wavered when he stood for the Liberals in Liverpool at the general election of 1885, and lost. Parnell, eager to secure for his party victory in a February 1886 by-election in Galway borough, and conscious of O'Shea's power to expose the affair with Katharine, recalled him to stand for Galway, steering him past horrified party colleagues and the existing party candidate, Michael Lynch. Thanks to Parnell's browbeating of the electorate, O'Shea was returned. However, he abstained from voting on the home rule bill (8 June), did not stand in the general election of July 1886, and largely retired from public life. He left Parnell damaged, prey to internal enemies, and living with the political time-bomb which O'Shea would explode in due course.
When Katharine became sole beneficiary of her aunt's revised will in 1888, the die was cast, but O'Shea held back in case the legacy might indirectly prove beneficial. With Aunt Ben's death (May 1889), he found no such consolation. Frustrated by the now public fact of Katharine's cohabitation with Parnell in Brighton, he filed for divorce on Christmas eve, naming Parnell as co-respondent. His action precipitated a classic Victorian scandal: Parnell's party rivals and hitherto respectable supporters expressed shock and outrage, as crucial backers, including Michael Davitt (qv), the catholic hierarchy, and the Gladstonian Liberals, were alienated. In addition to splitting the Irish party, O'Shea, who insisted that he had maintained contact with his family throughout, eventually won his decree nisi in November 1890 with custody of all the children under 16, including Parnell's daughters Katie and Clare (subsequently transferred back to Katharine). His ex-wife married the disgraced Parnell near Brighton in June 1891, where he died of exhaustion in October after trying desperately to save his political career. When Katharine's aunt's will, contested by her siblings, was settled in court in March 1892, Katharine's claim prevailed. O'Shea gained little but a token interest, especially after costs and dependants were provided for. Hounded by the press, he subsequently lived in obscurity with his share of the children in Brighton, where he died 22 April 1905, aged 65, and was buried at Hove cemetery. His son, Gerard, briefly noteworthy as adviser to the 1937 Hollywood film Parnell, based on a play by Elsie T. Schauffer to which he had raised personal objections, died in 1943. O'Shea's daughters had both died in the early 1920s.