Farrell was born and raised in the Convent Road area of Dalkey and was educated at Harold Boy's National School and the Christian Brothers in Dún Laoghaire, which he won a scholarship to.

During his time with the club his teammates, apart from Eglington, also included Alex Stevenson, Peter Corr, Harry Catterick, Wally Fielding, Tommy E. Jones, Brian Labone and Dave Hickson.

He managed Pats in their 1967–68 Inter-Cities Fairs Cup ties against FC Girondins de Bordeaux but resigned in March 1968.

Both associations, the Northern Ireland–based IFA and the Ireland–based FAI claimed jurisdiction over the whole of Ireland and selected players from the whole island.

He scored his second goal for the FAI XI on 9 October 1949 a in 1–1 draw with Finland, a qualifier for the 1950 FIFA World Cup.

Together with Johnny Carey, Con Martin, Bill Gorman, Tommy Eglington, Alex Stevenson and Davy Walsh, he was one of seven players born in the Irish Free State to play for the IFA XI that day.

Farrell also helped the IFA XI gain some other respectable results, including a 2–0 win against Scotland on 4 October 1947 and a 2–2 draw with England at Goodison Park on 5 November 1947.