In international play O'Hanlon shared 1st with Max Euwe at Broadstairs in 1921, took 8th at the Hastings International Congress in 1921/22 (Boris Kostić won), tied for 1st–3rd with Marcel Duchamp and Vitaly Halberstadt at Hyères in 1928, and took 12th at Nice 1930 (Savielly Tartakower won). He also played for Ireland in unofficial and official Chess Olympiads at Paris 1924, Warsaw 1935 and Buenos Aires 1939.
He had been in poor health which had prevented his taking part in tournament play for a number of years, but at the time of his death he was overhauling his opening repertoire in preparation for the 1961 Irish championship! After his death a series of five tournaments in his memory were played at the Dublin Chess Club from 1960 to 1965 where he had been a member. O'Hanlon was popular with Irish players and non-players alike as well as players in places like Hastings, Amsterdam, Moscow, Prague and Munich because of his gentlemanly manners. In his youth he was an oarsman who won trophies at regattas all over Ireland. In addition, he was also a strong long distance swimmer.
The Irish Chess Union was founded in 1912 and O'Hanlon won the first two. He played in every championship, except in 1927, from 1913 to 1956 and on his last appearance he was eighty years old.
The First Irish Chess Union Championship was held in 1913 even though there had been a competition for the title during the period 1865 to 1893 when a number of different organizations had organized Irish Championships. O’Hanlon was the champion of Ulster, a title he had had held since 1902, and he played regularly in England. As a result of his play in England he had contact with the German master (who was a resident in England for many years) George Shories and towards the end of 1912 they played a series of 19 friendly games while Shories was on a visit to the North of Ireland. O’Hanlon won 7, drew 1 and lost 11. It was those games that sharpened O'Hanlon's play and prepared him for his attempt to win the Irish championship in 1913.
Originally it was intended that the provincial champions would play a double round round robin to decide the challenger to the current champion, but it turned out that only two players showed up. So, O'Hanlon played a match of five games against a fellow named C. J. Barry at the Dublin Chess Club which he won and with the match victory, the right to challenge the champion, Porterfield Rynd.
Rynd had first won the Irish title in 1865 and had held it since that time, except between 1886 and 1892. Rynd was retired from chess, but came out to play O'Hanlon. Porterfield Rynd was never exactly a household name in chess, but at the height of his powers in 1888 he he defeated Amos Burn by 3 to 1 in a match and then scored +2 –2 =1 against James Mason.
Apparently Rynd's heart was not in the match which only lasted three games. Rynd, who was in his mid-sixties clearly was no longer the player he had once been and did not have the concentration required for a serious match, played the games very quickly. The time limit was sixty minutes for fifteen moves, but Rynd only used 10 to 20 minutes per game and, of course, made a lot of mistakes and O'Hanlon wiped the floor with him, won the match and the title of Irish Champion and went on to be the dominating force in Irish chess for decades to come.
In the following game O'Hanlon's opponent gets mauled.