Terence O’Brien was one of the best oarsmen of his day who was not a University Blue. At the age of 18, he was stroke to the London Rowing Club (LRC) eight in the Grand Challenge Cup at Henley in 1925, and was stroke again the following year when LRC won the first Head of the River Race. It was the first of 10 consecutive wins for the London club. In 1927 O’Brien was again in the LRC boat in the Grand, but they were beaten by Thames RC. O’Brien, however, won the Silver Goblets that year with Archie Nisbet, who he had teamed up with in 1925. Due to O’Brien being hampered with stitches in a thumb, they lost in their first heat while trying to defend their title against Jack Beresford and Gordon Killick in 1928. Nisbet and O’Brien, however, were still selected for the coxless pairs at the 1928 Amsterdam Olympics. Having set an Olympic record of 7:56.2 in their opening heat, they went all the way to the final when, despite a good performance against the German pair of Bruno Müller and Kurt Moeschter, they had to be content with the silver medal.
O’Brien was elected captain of LRC and became a member of the executive committee of the Thames Amateur Rowing Council in 1929. That same year, he was also stroke to the coxless fours that reached the Steward’s Challenge Cup at Henley only to lose to First Trinity. He won the Wyfold Challenge Cup at Henley in 1930 with the fours but also had the honour of being stroke to the eights that won the Grand for the first time since 1890. Also in 1930, O’Brien won a gold medal in the England boat that won the eights at the inaugural British Empire Games in Canada.