Treacy attends St. Anne’s Post-Primary School in Cappoquin, County Waterford, running more than seven miles to school every morning. He graduates from Providence College in Providence, Rhode Island. In 1978 and 1979 he wins the IAAF World Cross Country Championships in Glasgow, Scotland and Limerick respectively.
Treacy is known as a tenacious runner who does not have an especially sharp final kick in track races. In the 1978 European Athletics Championships in Prague, he places 11th in the fast 10,000-metre race and fourth in the slow and tactical 5,000-metre race, losing to Italy‘s Venanzio Ortis by just three tenths of a second. In the 5,000-metre final, he lingers behind Great Britain‘s Nick Rose on the final back straight just after Rose drops from the lead group.
In the 1980 Summer Olympics in Moscow, Treacy collapses in his 10,000-metre heat with only 200 metres left, a victim of heat paralysis and dehydration. Because he was running in fourth place when he collapses and because only the top four runners qualify directly for the final from the three heats, his collapse allows Finnish four-time Olympic champion Lasse Virén, who had been trailing him, to qualify directly for the final. Having recovered from his heat-induced collapse, Treacy places seventh in the 5,000-metre final of those Olympics.
In the 1984 Summer Olympics in Los Angeles, California, Treacy places ninth in the 10,000-metre final before crowning his athletics career with a silver medal in the men’s marathon. Winner Carlos Lopes of Portugal is largely unchallenged for much of the race, with Treacy down the field until entering the top six around the 20-kilometre mark. He continues to work his way up the rankings until entering Los Angeles Memorial Coliseum just behind second-place English athlete Charlie Spedding. He overtakes Spedding with 150m to go, during which the Irish television commentary of Jimmy Magee lists the previous Irish Olympic medal winners up to that time, before culminating, “And for the 13th time, an Olympic medal goes to John Treacy from Villierstown in Waterford, the little man with the big heart.” His silver medal places Ireland 33rd on the medals table.
After the Los Angeles Olympics, Treacy runs competitively until 1995, retiring following a road race held in his honour in Waterford, attended by the other two medalists from the 1984 Olympic marathon, Carlos Lopes and Charlie Spedding. While he does not win any more major international championships medals, he does win the 1992 Los Angeles Marathon. At the 1986 European Athletics Championships in Stuttgart, he places sixth in the 10,000-metre race. In the 1987 World Championships in Athletics in Rome, he places twenty-sixth in the 10,000-metre race and thirteenth in the 5,000-metre final. He fails to finish the marathon at the 1988 Summer Olympics in Seoul and places 51st in his final Olympic games, the 1992 Summer Olympics in Barcelona in 1992. He wins the 1993 Dublin Marathon.
Treacy is currently chief executive of Sport Ireland, a statutory authority that oversees, and partly funds, the development of sport within Ireland . He is married to Fionnuala and they have four children: Caoimhe, Deirdre, Sean, and Conor.