Quinn grew up in Cabinteely, Co. Dublin, in what he described as "humble" circumstances. His father, Murty, was a musician and singer, and Quinn, who was educated at Clonkeen College, started out as a pop group drummer and guitarist. In 1988, he emigrated to the US with his mother Bernadette, and sisters Sonya, and Louisa.
Quinn did commercials for Pepsi and Ray-Ban, appeared in the music video for the Richard Marx song "Satisfied," and had his first speaking line in the pilot of Beverly Hills, 90210.
In 1991, Quinn had his first major role in the movie Shout. One of Quinn's more visible roles began in 1990 as the character Mark Healy in the sitcom Roseanne. He continued in this role until the show ended in 1997. In 2018, the fourth episode of the revived show's tenth season was dedicated to the memory of Quinn.
Quinn took on the role as youngest son Cedric on the 1992 U.S. and UK TV series Covington Cross. In 1992, he starred in the slasher film Dr. Giggles. In 1997, he played dual roles in the horror anthology film Campfire Tales.
Originally the character Doyle was American, but the producers of Angel liked both Quinn and his Irish accent so much they decided to make the character Irish. Quinn was pleased Doyle was made so because it would allow him to use his native accent: "I've been hiding it for so long that it's amazing to have some freedom. It was like putting on an old pair of shoes — it's bringing my soul back to life." The first Angel episode produced after his death, "Long Day's Journey," was dedicated in his memory.
With his television money, Quinn bought a half-share in the Los Angeles nightclub Goldfingers. His last film work was in R.S.V.P. (2002).
Quinn died on December 3, 2002 at a friend's home of a drug overdose. He was 32 years old.
Quinn was a series regular in the first ten episodes of Angel as the half-demon Doyle, although appearing in only nine of the first season. Other two episodes then featured archive footage that included him.
- "City Of"
- "Lonely Heart"
- "In the Dark"
- "I Fall to Pieces"
- "Rm w/a Vu"
- "Sense & Sensitivity"
- "The Bachelor Party"
- "I Will Remember You"
- "Parting Gifts" (Only credited)
- "Birthday" (Only in archive footage)
- "You're Welcome" (Only in archive footage)
- Glenn Quinn on Wikipedia