He then moved to the USA, to Brown University from which he earned a PhD in 1973, for a thesis on "Capacities in Uniform Approximation" done under Brian Cole.

[6] O'Farrell has long been active in the Irish Mathematical Society, serving as president in 1983 and 1984,[7] and as editor of the Bulletin of the IMS since 2011.

[9] These range from the Irish Mathematical Olympiad Manual[10] to undergraduate and postgraduate level texts and research monographs.

It starts at Dunsink Observatory in County Dublin, just west of the city, and follows the Royal Canal east to Broom Bridge.

In 2018, O’Farrell and Ó Cairbre received the 2018 Maths Week Ireland Award, for "outstanding work in raising public awareness of mathematics" resulting from the founding and nurturing the Hamilton Walk.