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 assistant puppeteer to Fred Rogers, working with him at WQED in Pittsburgh on Rogers’s noontime program, The Children’s Corner. Rogers and Coombs became close friends and when Rogers was offered a show in 1963 at the Canadian Broadcasting Corporation, he invited Coombs to join him in Canada to work 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 the Poor Alex Theatre in The Tickle Trunk, starring Mr. Dressup with Casey and Finnegan.

Coombs lived with his family in the city of Pickering. His wife Marlene ran a day care in Scarborough (east Toronto), called the Butternut Learning Centre. They had two children: Christopher and Catherine. 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.

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.

Coombs suffered a stroke on September 10, 2001, and died on September 18, 2001 at the age of 73. Coombs’s ashes were scattered at his camp in Maine.

On November 26, 2012, Google commemorated Coombs’ 85th birthday with a Google Doodle.