He declined the job offer, fearing it would create a dull future, but used the $2500 to open his own repertory theater in Saint Paul, Minnesota.

MGM required its younger players to take an extensive, time-consuming training course, described by Carlson's fellow MGM rookie Pinky Tomlin as "star school... 25 hours a day, eight days a week";[5] Tomlin declined the regimen and the contract to pursue his musical career, and it is likely that Richard Carlson also dropped out to continue his dramatic career.

[8] Carlson was the main male actor for such movies as Little Accident (1939), Beyond Tomorrow (1940), The Ghost Breakers (1940), The Howards of Virginia (1940), Too Many Girls (1940), No, No, Nanette (1941), Back Street (1941), West Point Widow (1941), The Little Foxes (1941), Secrets of G32 (1942), The Affairs of Martha (1942), Highways by Night (1942), and My Heart Belongs to Daddy (1942).

Carlson played in several movies for MGM in the early 1940s, including White Cargo (1942), Presenting Lily Mars (1943), A Stranger in Town (1943), Young Ideas (1943), and The Man from Down Under (1943).

In 1950, he co-featured with Deborah Kerr and Stewart Granger in the very successful adventure movie King Solomon's Mines, filmed on location in the Kenya Colony and the Belgian Congo.

While filming in Africa, Carlson wrote a series of articles for The Saturday Evening Post, collectively titled "Diary of a Hollywood Safari.

"[11] Despite the movie's success, Carlson remained a supporting actor: The Sound of Fury (1950), Valentino (1951), A Millionaire for Christy (1951), and The Blue Veil (1951).

Carlson played the lead in The Magnetic Monster (1953) which caused him to become popular in the newly re-emergent genres of science fiction and horror.

He starred in the educational science film The Strange Case of the Cosmic Rays, directed by Frank Capra for the acclaimed Bell Telephone Series in 1957.

In 1957 and 1958, Carlson played "Mr. Fiction Writer" in three of the nine educational features made for television collectively titled The Bell Laboratory Science Series.

In 1957 he was cast as two different clergymen, Rabbi Avraham Soltes and Father William Wendt, in the episodes "The Happy Gift" and "Call For Help", respectively, of the syndicated religious anthology series, Crossroads.

In 1959, Carlson was cast as Paul Drake in "The Faithless" of the NBC western television series Riverboat, with Darren McGavin.

In the story line, Drake is an escaped prisoner with medical training being transported on the river vessel, the Enterprise, back to jail.

Having lost his religious faith, Drake refuses to render medical assistance to a two-year-old girl stricken with a communicable disease which threatens the entire vessel.

In 1965, he played a mad scientist who creates a mutant, killer octopus in the Voyage to the Bottom of the Sea episode "The Village of Guilt".