However, at the weekend, he opened another chapter in his life when he swapped the red jersey for a three-piece suit to marry his sweetheart.
His first sport was hurling, but that all fizzled out, when aged 15, he enrolled in the privately run Rockwell College boarding school, where rugby was as important as the religion classes.
From then on he followed the school’s motto: “Constancy in the midst of change.”
Yesterday the former back row returned to the grounds of his old school where he walked down the aisle with Limerick native Gráinne Brosnahan.
Stars from the rugby world, and their beautiful partners and wives, attended the ceremony, including retired rugby All-Black and Munster winger Dougie Howlett and his New Zealand wife Monique.
“We are delighted to be here today. Weddings are great occasions and when it’s one of your good mates like this — to help celebrate in his day — there’s nothing better,” he said.
Famous faces from Munster’s first Heineken European Cup winning side were guests, including Jerry Flannery, Frankie Sheahan, Mick O’Driscoll, and Marcus Horan.
Ulster, Irish, and Lions hooker, Rory Best, was one of four groomsmen, along with Munster and Leinster’s Stephen Keogh, the groom’s brother Kevin and the groom’s best man, brother Ed. Former Irish rugby manager, Declan Kidney was also a guest.
Denis, from Cashel, wore a grey suit with dickie bow from Esquire in Limerick. He waited 45 minutes for his bride to arrive.
The couple met three years ago in Grainne’s native Limerick city.
Grainne arrived just before 2pm, driven in a black Mercedes — her proud father Clem by her side.
She looked stunning in a Mikaella ’50s-style one-piece lace dress with a veil which she got in Abheil of Adare, Co Clare.
Her bridesmaids, including sister Anne Marie, Lissie Hickey, Bridget Ryan and Laurie Hickey.
The couple will spend a few days in the Costa del Sol, before a second trip stateside later in the year to Chicago.
The reception took place in Dundrum House where beef, salmon, and sea bass were part of the menu.