Before entering films, Merrill's deep cultured voice won him a recurring role as Bruce Wayne / Batman in the Superman radio series.

[2] In 1958, Merrill guest starred with June Lockhart in the roles of Joshua and Emily Newton in the episode "Medicine Man" of the series Cimarron City.

Merrill had recurring roles in Then Came Bronson with Michael Parks and Young Doctor Kildare, both of which lasted less than a season.

In response to U.S. President Lyndon B. Johnson's Vietnam War policy, he unsuccessfully sought nomination to the Maine legislature as an anti-war, pro-environmentalist primary candidate.

[1] Merrill survived his second ex-wife, Bette Davis, by only five months, dying of lung cancer in Falmouth, Maine, on March 5, 1990.