World Rugby announced the death on Wednesday (Thursday NZT). The cause of death was not immediately known.
Halpin made 11 appearances for Ireland and was known for his gesture after scoring a try against New Zealand at Ellis Park in Johannesburg. Jogging backward, he raised two middle fingers at his opponents. The All Blacks went on to win 43-19.
Halpin made his international debut against England in 1990 and also played in the 1991 Rugby World Cup. He played club rugby for Leinster, London Irish and Harlequins.
He had more recently been working at Cistercian College in Tipperary.
“The College community of staff, students, parents and monks were devastated this morning on hearing of the sudden death of our much loved colleague and friend Gary Halpin RIP,” the school wrote on Twitter.
Halpin also competed in the hammer throw – for Manhattan College in the United States and for Ireland at the 1987 world track championships