Though slight of build and with a thin-faced appearance, Soule's diction and light voice established himself as a popular romantic lead in old-time radio anthologies and soap operas, including Bachelor's Children (1935-1946), as Sam Ryder, The Romance of Helen Trent (1933-1950s), as various suitors, sane and otherwise, and The First Nighter Program (1943-1952), as various leading men opposite Barbara Luddy, as well as parts on the adventure serials Jack Armstrong, All-American (as Coach Hardy) and Captain Midnight (as an OSS officer).
Moving on-camera in the late 40s and early 50s, the thin, bespectacled Soule was typecast as fussy or nebbishy clerks, officials, doctors, and employers, appearing in such films as The Day the Earth Stood Still and Hitchcock's North by Northwest. He had recurring television roles on Dragnet (as lab analyst Ray Pinker), The Andy Griffith Show (choir director John Masters), and Perry Mason (the court clerk), plus guest appearances on I Love Lucy, Gunsmoke and Simon & Simon. As a voice actor, Soule played Batman (as well as butler Alfred Pennyworth) in six different animated series between 1968 and 1979, with Casey Kasem as Robin, including Superfriends (later playing Professor Martin Stein when Adam West took over as Batman). His other voice credits include the father in the Disney Christmas featurette The Small One and various parts in the surreal French animated feature Fantastic Planet.