Henry, Denis Stanislaus (1864–1925), lawyer and politician, was born 7 March 1864 in Cahore, Draperstown, Co. Londonderry, one of five sons and two daughters of James Henry, businessman, and Ellen Henry (née Kelly), both of Draperstown. Educated at the local national school, he attended the Marist College in Dundalk, before enrolling at the age of fourteen in the Jesuit College of Mount St Mary's near Chesterfield, Derbyshire, England. He subsequently read law at QCB, where he won every available law scholarship possible, before being called to the Irish bar in 1885. Henry established himself as a successful figure in the north-west circuit, becoming a QC in 1898.
Like so many prominent lawyers of this era, he was closely involved with politics. While at one time a firm liberal, he declared his support for the unionist cause when Gladstone endorsed home rule in 1886. Henry's early participation in politics was active and varied. He supported unionist candidates in the 1895 election in Derry South and Donegal East, while his latter endorsement provoked a form of scornful contemporary criticism from nationalists which was to feature in his early life. A unionist delegate at the inaugural meeting of the Ulster Unionist Council in 1905, Henry became unionist candidate in the Tyrone North election of 1906, losing the contest by nine votes. Rejecting the legal advice for a recount, he accepted defeat with characteristic good grace. In 1907 his attempt to win Tyrone North in a by-election witnessed bitter defeat by a mere seven votes. His commitment to the union, and his warm personality, won Henry much admiration and respect from contemporaries of all political outlooks.
He rapidly emerged as one of the most outstanding advocates in Ireland, becoming father of the north-west circuit as well as establishing a successful practice in the Four Courts. In 1898 he had the unusual experience of appearing in three murder cases at a single assize, in which convictions were recorded. In January 1914 Henry, along with S. L. Brown (qv), KC, headed a commission of inquiry into the circumstances of the riots that followed the Larkinite demonstration in Dublin in August 1913. Henry's quiet, courteous, and economical courtroom manner was evident during the proceedings. W. E. Wylie (qv) regarded Henry as the quickest thinker and most brilliant advocate that he had known, while A. M. Sullivan (qv) (1871–1959) recalled that Henry was the best man that the Irish bar had produced in his time. In August 1916 Henry formed part of a royal commission of inquiry into the deaths of Francis Sheehy-Skeffington (qv) and two other men during the Easter rising. The commissioners found no possible justification for the conduct of Capt. John Bowen-Colthurst (qv), the officer responsible.
By this stage Henry had entered parliament, having won the Londonderry South by-election in May 1916. He was soon promoted to Irish law officerships: solicitor general in 1918, and attorney general in 1919. From then until August 1921, he served two Irish chief secretaries: Ian MacPherson (qv) and Sir Hamar Greenwood (qv). His tenure was as troublesome as it was eventful. Badly briefed, and with Greenwood often absent from the commons, he at times appeared defensive when answering questions about allegations of misconduct by crown forces during the Anglo–Irish war, the revelations of reprisals, and the application of coercive measures such as the ‘drumhead’ courts. Henry was unrepentant in his vindication of government policy, and in cabinet opposed making truce offers to Sinn Féin. In spite of many heated parliamentary debates, he maintained good personal relations with all sides of the house. Testimony that Henry's reputation remained intact came with his appointment in August 1921 as the first lord chief justice of Northern Ireland. The truce in the Anglo–Irish war and the prospects of formal negotiations between Sinn Féin and the British government dominated the political agenda, which partly explains why unionists made little play with the fact that the newly created state had a catholic leading the judiciary. In an atmosphere of uncertainty about the stability of the northern state, nationalists speculated that Henry's appointment would be short-lived.
Henry left Westminster for the last time on 5 August 1921, vacating his Londonderry South constituency that he had retained in the 1918 general election. Sworn in as lord chief justice on 15 August, he was charged with the task of assembling the machinery of a new judiciary at a time of great lawlessness. All aspects of the workings of the new judiciary fell to Henry, who displayed great energy and initiative, applying his notable qualities of working with others to good use. He secured the use of the county courthouse, Crumlin Rd, Belfast, as temporary accommodation for the supreme court. He was directly involved in the recruitment of officials to staff the new judiciary, adopting a policy originated by the prime minister, Sir James Craig (qv), that when candidates of equal merit were considered, the deciding qualification should be that the applicant was Ulster-born. Even the more mundane tasks of ensuring adequate pension rights for newly appointed staff and the purchase of furniture came under Henry's brief. He worked hard to foster good relations with members of the northern bar, who accepted an invitation to dine with Henry and his other judges in June 1922. He was also at the centre of several notable cases, which reflected the turbulent times in which the northern state functioned in its early years. In July 1922, Henry ruled against the plaintiff in the case of O'Hanlon v. Governor of Belfast Prison, which mounted a challenge to the legality of the special powers act. In November 1923 he ruled against claims for compensation for the victims arising out of the well-publicised Cushendall ambush of 23 June 1922, arguing that the deaths of the three catholic youths arose out of unlawful assembly. The cumulative impact of his work after 1919 took its toll, and he died 1 October 1925 at his home, Lisvarna, Windsor Avenue, Belfast, and was buried at the family plot in Straw cemetery in Draperstown.
He married (1910) Violet, third daughter of Hugh Holmes (qv), lord justice. They had five children: James, Denise, Alice, Denis, and Lorna.