His work was part of the painting event in the art competition at the 1928 Summer Olympics.
For a time after his mother's death, he was raised by his aunt Charlotte Grace O'Brien, along with his sisters, Nelly and Lucy.
His son Brendan, a surgeon in Dublin, married artist Kitty Wilmer O'Brien.
In 1887, O'Brien visited galleries in Italy and then enrolled at the Royal Academy in Antwerp.
O'Brien was designated an associate of the Royal Hibernian Academy in 1906, a member in 1907, and was later president between 1910 and 1945.