During World War II, Greene served as a Flying officer in the Royal Canadian Air Force.

Greene left the CBC and became a freelancer after the war when the network ordered staff announcers to turn over a large percentage of any income they earned from film narration.

In 1955, he was Ludwig van Beethoven in an episode of the TV version of You Are There, and also appeared as Marcus Brutus in Julius Caesar at the Stratford Festival.

The first of his continuing TV roles was as the patriarch Ben "Pa" Cartwright in Bonanza, the first one-hour Western series filmed in colour (1959–1973), making Greene a household name.

When it failed to gain sufficient ratings and was cancelled after 13 episodes, Greene thereafter hosted the syndicated nature documentary series Last of the Wild from 1974 to 1975.

Greene's typecasting as a wise father character continued with the 1981 series Code Red as a fire-department chief, whose command includes his children as subordinates.

He appeared in the 1986 HBO mockumentary The Canadian Conspiracy, about the supposed subversion of the United States by Canadian-born media personalities.

For nearly a decade, Greene co-hosted the Macy's Thanksgiving Day Parade on NBC with Betty White.

[9] Greene died on 11 September 1987, aged 72, from complications from pneumonia, following ulcer surgery, at Saint Johns' Hospital in Santa Monica, California.

[13] Greene was made an Officer of the Order of Canada on 28 October 1969, "for services to the Performing Arts and to the community.

"[14] Greene was awarded an honorary doctor of laws degree by his alma mater, Queen's University, in 1971.

The school trained a number of future broadcasters and actors including Leslie Nielsen, James Doohan, Les Rubie, Gordie Tapp, Fred Davis, Billie Mae Richards, William Davidson, Alfie Scopp, Murray Chercover, Jonathan Frid, Cec Linder, Les Lye, Bill Luxton, and Roy Currie.

Its faculty included many CBC staff such as Mavor Moore, Fletcher Markle, Lister Sinclair, Andrew Allan, and Esse Ljungh, and graduated a total of 381 students in seven years, 90% of whom found work in the industry.