Playing his first games for Wexford RFC at the age of eleven he was educated at Clongowes Wood College, helping them win the Leinster Senior Cup in 1998. He was capped for Ireland at Schools, U19s and A level but made his senior debut as a replacement in a pool game against Romania in the 1999 Rugby World Cup.
The struggle for form saw D’Arcy return to playing for the U21s, however, at the start of 2004 he again caught the eye of Eddie O’Sullivan and earnt a recall to the senior side. He went on during that Championship to help Ireland to gain the Triple Crown with two tries and he was named as BBC Player of the Six Nations that year.
Whilst he was hampered by injury in 2004-5 season, he was selected for the British & Irish Lions in 2005 to Tour New Zealand where he played in the games against Argentina, Bay of Plenty, NZ Maori, Otago, Southland, Manawatu and Auckland.
In the 2006-7 season again saw him exert his influence over the Irish side, however, despite the severe arm injury that he picked up in 2008 he has returned to Kidney’s Irish set up in the 2009 6 Nations, scoring a try on his return against France.