Mahony, Harold Sigerson (1867–1905), tennis player, was born 13 February 1867, probably in Edinburgh, only son of Richard John Mahony (1828–92) of Dromore Castle, near Kenmare, Co. Kerry, JP and high sheriff (1853), and his wife Mary Harriette, eldest daughter of John Waller, barrister, of Shannon Grove, Pallas Henry, Co. Limerick. Harold's second name derived from the surname of his paternal grandmother, Lucinda Catherine Segerson. Educated at TCD, he inherited the family estates in Kerry in 1892. As a member of the Fitzwilliam club in Dublin, he had already made his name as a gifted lawn-tennis player at a time when the amateur sport was burgeoning all over Europe and America. Between 1891 and 1903 he advanced to the semi-finals, and sometimes to the finals, of the men's singles at Wimbledon in eight of the twelve annual competitions entered. He achieved similar levels of success three times in the men's doubles at Wimbledon. In 1891 his fellow club-member, Joshua Pim (qv), defeated him in three sets in one of the semi-finals of the Wimbledon men's singles. That year he also reached the semi-finals of the men's doubles. When he played with Pim in the men's doubles at Wimbledon in 1892, the pair were beaten over five sets in the final. Pim soundly beat him over three sets in the Wimbledon men's singles final in 1893. With Charlotte (‘Chattie’) Cooper, Mahony won the All-England mixed doubles title in 1894 (and was mixed doubles champion for the next four years). He had gained some renown as an agreeable and astute coach by this stage, and Cooper (several times Wimbledon ladies’ champion) credited his lessons for developing her tactical ability; he urged her always to ‘smash at a woman's feet’ (O'Connor, 10).
Tall, slim, and neatly moustached, with easy manner and dark good looks, Mahony tended to attract numbers of aspirant female players. In 1895 he won the Irish mixed doubles. His first major success came at Wimbledon in 1896 where he won the men's singles, beating W. V. Eaves decisively in three sets, and following up with a more closely fought victory over Wilfrid Baddeley in the customary challenge round (in which the previous year's champion was entitled to play the new titleholder). He won the Irish mixed doubles again in 1896. In the challenge round of the men's singles at Wimbledon in 1897 he was outplayed in three sets by the great Reginald Doherty (1874–1910). He reached the men's doubles semi-finals that year. Undertaking a tennis tour of the USA in the summer of 1897, he was defeated once only, in the finals of the US men's doubles. After a tough battle he was beaten in the Wimbledon men's singles final of 1898 by Reginald's brother Hugh Doherty (1876–1919). Having overcome chronic deficiencies in his forehand (which he usually made up for by quick-wittedness in other areas of play and a lethal volley) he managed to defeat Reginald Doherty in the Irish championships that year. Put out of Wimbledon in the men's singles semi-finals in 1899, he won the men's singles at the German Open months later. Selected for the British team attending the Paris Olympics of 1900 (though professing a mild Irish patriotism), he won two silver medals and one bronze, one of very few Irish athletes ever to manage the feat of capturing multiple medals in one games (or indeed at more than one). His old adversary Hugh Doherty beat him in the men's singles final. The Doherty brothers beat Mahony and A. J. Norris in a semi-final of the men's doubles. Mahony and Hélène Prévost were defeated in the mixed doubles final. He reached the men's singles semi-finals at Wimbledon in 1901 and 1902, was runner-up in the men's doubles final in 1903, and was chosen to represent Great Britain in the (third) Davis Cup competition of 1903. He was also a skilled musician. Cycling home after a meal at the Caragh Lake hotel, near Dooks, Co. Kerry, on the night of 28 June 1905, he hit a stone at the base of a hill and was flung off his bicycle, breaking his neck. He was buried in the family burial ground at Templenoe, Co. Kerry. He never married.