Newfield entered the movie business in 1919 and began directing comedy shorts in 1926 with Jane's Engagement Party and Jane's Predicament. He moved into full-length features in 1933 with Reform Girl and Important Witness and was quickly snapped up by the burgeoning B-movie production houses of the era, most notably Tower, Ambassador, and PRC. The latter, under the aegis of his brother Sigmund, provided Newfield with so much work that he was forced to adopt two pseudonyms — Sherman Scott and Peter Stewart — in order to make his output seem more reasonable.
Newfield was a specialist in fast, low-budget filmmaking; he relied heavily on stock footage shot well ahead of time, which he reused shamelessly. He was a specialist in crime and action films, but that didn't keep him from doing the occasional comedy (Skipalong Rosenbloom — a parody of Hopalong Cassidy starring ex-prize fighter Maxie Rosenbloom), serious drama (I Accuse My Parents, cited by author Wheeler W. Dixon in "The 'B' Directors: A Biographical Directory" as the antecedent to Rebel Without a Cause), exploitation picture (Devil's Weed), or horror or science-fiction vehicle (The Monster Maker, Dead Men Walk, The Flying Serpent, and The Lost Continent). The film he is best remembered for is The Terror of Tiny Town, a musical Western featuring a cast of all little people.
Although hardly noted for quality, Newfield's films were effective within their budgets and shooting schedules (sometimes as little as three days), and with the right cast — such as veteran horror film heavy George Zucco, a regular Newfield villain — he could get good results. His movies were popular program fillers, especially with baby boomers, who got to see them either in the waning days of B-pictures or the early days of television, and his science fiction and horror films of his are among the most familiar in the B-movie category — and four of Newfield's films were staples in the programming of Mystery Science Theater 3000 in the '90s. 
- The Mad Monster (Experiment #103) - Director
- Lost Continent (Experiment #208) - Director
- I Accuse My Parents (Experiment #507) - Director
- Radar Secret Service (Experiment #520) - Director
- In an early riff during Radar Secret Service, Tom Servo identifies Sam Newfield at the director of I Accuse My Parents and Jungle Goddess. However, Jungle Goddess is credited to director Lewis D. Collins. Servo may have been confusing it with Lost Continent. Joel made a similar error during the credits of I Accuse My Parents.