Furlong comes from a farming family in the parish of Horeswood in County Wexford.[2] He started his rugby playing underage at New Ross RFC in County Wexford.
Furlong made his senior debut for Leinster Rugby in November 2013 as a replacement against the Dragons.[4] He was part of the Leinster A team which won the 2013–14 British and Irish Cup.[5][6] Ahead of the 2014–15 season, Furlong was promoted from the Leinster Academy to the senior squad.[7]
In 2021 Furlong was selected to World Rugby's Dream Team of the Year.[8]
International career
Ireland
Furlong made his Ireland senior debut on 29 August 2015 against Wales in a warm-up game for the 2015 Rugby World Cup.[9]
He was named in the Ireland squad for the World Cup on 1 September 2015.[10][11]
In November 2016, Furlong started for Ireland in the Autumn Internationals, including the historical victory over New Zealand on 15 November 2016.[12] He also played for Ireland in the 2017 Six Nations Championship.[13]