O'Brien, Sir Timothy Carew (1861–1948), 3rd baronet, international cricketer for England and Ireland, was born 5 November 1861 in Dublin, eldest son among three sons and a daughter of Timothy O'Brien and Mary O'Brien (née Carew O'Dwyer) of Dublin. His grandfather, Sir Timothy O'Brien, a Dublin merchant who had been MP for Cashel and lord mayor of Dublin, was created a baronet on the occasion of Queen Victoria's visit to Ireland in 1849. The family seat was at Lohort Castle, near Mallow, Co. Cork, and O'Brien played cricket in Ireland for Cork County, Na Shulers, and Phoenix CC. He was educated at two catholic schools in England – Downside School near Bath, and St Charles's College, Notting Hill – and later attended New Inn Hall, Oxford. He made his first-class cricket debut for Middlesex against Gloucester (1881), and went up to Oxford (1884) reputedly with the sole intention of obtaining a blue. He succeeded in his aim and played for Oxford against Cambridge in both 1884 and 1885. O'Brien's initial blue (June 1884) was not auspicious, however, as he was bowled out for a pair. In contrast, his first game for the university the previous month resulted in a batting performance of 92, which was in large measure responsible for a seven-wicket victory over the touring Australians, Oxford's only victory to date against them. That same year he hit 72 for the MCC in another victory over Australia. Such form earned him an international call-up and he played in five tests for England between 1884 and 1896. Although he was not quite of test cricket standard, O'Brien was one of the top ‘gentleman’ (amateur) players of his era, playing 156 first-class matches for Middlesex, traditionally one of the strongest English counties, during 1881–98, and scoring 7,377 runs, including ten centuries (average 29.62). Among his most famous teammates were the legendary W. G. Grace – with whom he played for Middlesex and Grace's own cricket XI – and the great all-rounder C. B. Fry.
He went on two England cricket tours: to Australia under the captaincy of George Vernon (1887/8) and to South Africa under Lord Hawke (1895/6). O'Brien captained England in the first test of the latter tour against South Africa in Port Elizabeth when Hawke was taken ill, and he led England to a 288-run victory. Hawke actually played in that game but obviously was not well enough to captain the side. In batting terms O'Brien's England career was not particularly successful; he only managed 59 runs in total, giving him a disappointing batting average of 7.37. He later had the distinction of captaining his native country when he led Ireland in its inaugural first-class match against London County (May 1902), and continued to play for Ireland till 1907. In five first-class matches for Ireland he scored 306 runs, giving him an impressive average of 43.71. His highest score for Ireland was 167 against Oxford University in 1902. In his final first-class match in July 1914, at the age of 53, he bowed out of top-level cricket with a batting performance of 90 and 111 against Oxford University. He was primarily a middle-order batsman and was described as a dashing player who used his height and powerful build to good effect. As an amateur he tended to attack every ball bowled at him, sometimes with spectacular results, but it was a high-risk strategy. His most memorable performance on the cricket field was his 100 runs in eighty minutes – 83 of those in just thirty-five minutes – against Yorkshire in June 1889 when Middlesex had to make 280 runs in little more than three and a half hours. Middlesex eventually won by four wickets with just ten minutes to spare. O'Brien had also posted 92 in the first innings. All told, in 266 first-class matches he scored a total of 11,397 runs, by some distance the highest first-class total by an Irish cricketer, scoring fifteen centuries, and having a highly respectable batting average of 27.01. He hit 1,000 runs in a season on three occasions, his best being a total of 1,150 (average 27.38) in 1884. His only double century was 202 for Middlesex against Sussex at Hove in 1895.
O'Brien became 3rd baronet in 1895, on his uncle's death. He also had a military career: initially a lieutenant in the Derbyshire Yeomanry (1898–1900), he rose to the rank of captain in the 5th Battalion (militia) of the Royal Irish Fusiliers, and served with the remounts during the first world war, when he was an hon. major in the army. O'Brien died 9 December 1948 in Ramsay, Isle of Man. A brother, John George O'Brien (1866–1920), was also a cricketer, playing for Herefordshire and Ireland; and O'Brien's brother in law, C. E. de Trafford, played cricket for Warwickshire and Leicestershire.
O'Brien married (1885) Gundrede Annette Teresa de Trafford (d. 1952), they had two sons and eight daughters. The elder son, Timothy John Aloysius O'Brien (1892–1916) was killed in action during the Somme campaign as a lieutenant in the Royal Field Artillery, and it was Robert Rollo Gillespie O'Brien (1901–52) who succeeded his father to the baronetage. The family had its share of tragedy: three of O'Brien's daughters died relatively young, including the eldest daughter, Sicele, who perished in an air crash in 1931.