Ernest Coombs was born in Lewiston, Maine, and pursued a career in children's entertainment after attending North Yarmouth Academy in Yarmouth, Maine. He was an understudy to Fred Rogers. He travelled to Canada in 1963 to work for the Canadian Broadcasting Corporation on an early version of Mister Rogers' Neighborhood, called Misterogers. Rogers moved back to the United States three years later, but Coombs decided to stay in Canada, joining a new TV series called Butternut Square. Butternut Square ran from 1964 to 1967. During the run, Coombs appeared as the character in a stack show at the Poor Alex Theatre.
After Butternut Square ended, Coombs developed Mr. Dressup, which became one of English Canada's longest-running and most beloved children's programs. As Mr. Dressup, he presented arts and crafts, songs, stories and games for children with his friends Casey and Finnegan, a child and a dog who lived in a treehouse in Mr. Dressup's back yard. Casey was given a unisex name intentionally, because the character's childlike voice left Casey's gender ambiguous. Over the years, when viewers would ask Coombs whether Casey was a boy or a girl, he would ask, "What do you think?" However the questioner responded, he would say, "You're right!"
Later in the series, when the show's principal puppeteer, Judith Lawrence, retired, Casey and Finnegan were replaced by a small cast of anthropomorphic animal puppets. Coombs believed in gentle, wholesome children's programming that encouraged kids to use their creativity and imagination. In each episode, Mr. Dressup would dress up in a costume from his Tickle Trunk, and lead children in an imagination game. Many times his puppets would appear in costume as well.
The series continued production until its final taping in February 1996, when Coombs retired. Repeats continued to be shown on CBC Television until they were discontinued in 2006.
After retirement, Coombs continued to work as an entertainer, playing roles in Ross Petty's Christmas pantomimes of Peter Pan, Cinderella, and Aladdin, narrated a 2002 Canadian revival of the British animated television series, Simon in the Land of Chalk Drawings, and acted as a spokesman for children's charities.
Coombs also did a travelling stage show called "Tales from the Tickle Trunk." In this show he would share stories about the making of the Mr. Dressup show, as well as the origins, and fates, of some of the characters.
Coombs lived with his family in the city of Pickering. His wife Marlene ran a day care in Scarborough (east Toronto), called the Butternut Day Care. They had three children: Christopher, Kenneth, and Catherine (Minott). Marlene was killed in a traffic accident in 1992; she was walking on the sidewalk of Yonge Street in Toronto, when a car hit her. The driver may have had a seizure, resulting in a loss of control of the vehicle.
Coombs became a Canadian citizen in 1994. In 1996, he was named a Member of the Order of Canada.
Coombs suffered a stroke on September 10, 2001, and died on September 18, 2001 at the age of 73.
Coombs was cremated and his ashes scattered at his cottage in Maine.1989: A Lifetime Achievement Award from the Children's Broadcast Institute.
1994: The Academy of Canadian and Television's prestigious Earle Grey Award, for excellence in Canadian television programming.
1996: Appointed as a Member of the Order of Canada.
1996: Gemini for best performance in a children's program.
1997: Save the Children Award, for his many years of service as spokesperson for the Canadian Save the Children Foundation.
2001: An honorary doctorate of laws by Trent University in Peterborough, Ontario.
A tribute was made to Coombs in the Canadian television show The Latest Buzz, where the school for which the show is set is named Ernie Coombs High.
On November 26, 2012, Google commemorated Coombs' 85th birthday with a Google Doodle.
Chris Whiteley wrote and recorded a song entitled "The Week That Ernie Died" as a tribute to Ernie Coombs.