Farrelly was born in Cabra, Dublin, but was raised in North Great George's Street, Dublin. Farrelly's father, Mark, was an amateur bodybuilder. Farrelly speaks fluent Irish, having attended Scoil Caoimhin Primary and Secondary School, a Gaelscoil. He sang in the Palestrina Choir until the age of thirteen, as part of which he appeared on both the Christmas Late Late Show and Live at Three. He played Gaelic football for the Erin's Isle team where he was declared Sportstar of The Month. He also played rugby for the National College of Ireland, where he gained a National Diploma.
Farrelly is a former IT technician. He also worked as security for a nightclub which led to him occasionally working personal security for Bono and Larry Mullen, Jr. of U2 as well as Denise van Outen