In a career spanning more than four decades, Holt is best remembered for his roles in the films The Magnificent Ambersons (1942) and The Treasure of the Sierra Madre (1948).

[6] Instead he made his debut as Anne Shirley's suitor in Stella Dallas (1937) for Sam Goldwyn – the same role that another film star's son, Douglas Fairbanks Jr., had played in the 1925 version.

He lent Holt to Paramount to play the juvenile lead in Sons of the Legion[10] then RKO asked for him again in The Law West of Tombstone, supporting Harry Carey.

Holt later recalled, "I believe George O’Brien quit over money so RKO needed another Western star and I was put forward.

"[22] In early 1940, RKO announced Holt would make six low-budget B-Westerns, starting with Wagon Train with Martha O'Driscoll.

While Hopalong Cassidy was always the foreman of the Bar 20 Ranch, Tim played a cowboy, a Treasury agent, a Texas Ranger, or a number of other occupations.

[3] The Westerns proved popular and Holt wound up making six more: The Bandit Trail (1941), Dude Cowboy (1941), Riding the Wind (1942), Land of the Open Range (1942), Come on Danger (1942) and Thundering Hoofs (1942).

Holt's career received a boost in September 1941[26] when Orson Welles cast him as the lead in his second film, The Magnificent Ambersons (1942).

[30]) RKO announced they had purchased two stories for Holt, Five of Spades (which became The Avenging Rider) and Adventures of Salt Valley.

[31] Holt was going to enter the army, so RKO quickly put him in six more Westerns: Bandit Ranger (1942), Red River Robin Hood (1942), Pirates of the Prairie (1942), Fighting Frontier (1943), Sagebrush Law (1943) and The Avenging Rider (1942).

Holt became a decorated combat veteran of World War II, flying in the Pacific Theatre with the United States Army Air Forces as a B-29 bombardier.

Now he exuded a steady, serious no-nonsense type of mature cowboy who was less impulsive, more contemporary, and somewhat ‘world weary.

"[3][38] Tom Stempel argues that "While Holt had lost his baby fat during the war, he still had a wonderful grin and cute dimples.

For RKO he appeared in a series of Zane Gray adaptations: Thunder Mountain (1947),[39] Under the Tonto Rim (1947) and Wild Horse Mesa (1947).

[40] Holt was next borrowed by Warner Bros for the role for which he is probably best remembered — that of Bob Curtin to Humphrey Bogart's Fred C. Dobbs in John Huston's The Treasure of the Sierra Madre (1948), about two men who team up to prospect for gold, only to have greed tear apart their partnership.

Tim Holt tended to be outshone in reviews by Bogart and Walter Huston, the latter winning an Oscar for Best Supporting Actor for his performance.

Unlike Hopalong Cassidy's young sidekick Lucky, who just mooned after girls, Chito was active, which was a lot more interesting to watch, especially with Tim's reactions.

Chito performed the crucial functions of a B western movie sidekick: he was somebody with whom the hero could discuss the plot, and he provided some comedy relief.

Dore Schary left RKO in 1948 and the new management was not keen to cast Holt in anything other than Westerns: Rustlers (1949), Stagecoach Kid (1949), Masked Raiders (1949), The Mysterious Desperado (1949) and Riders of the Range (1949).

[45] The Westerns continued: Dynamite Pass (1950), Storm over Wyoming (1950), Rider from Tucson (1950), Border Treasure (1950) and Rio Grande Patrol (1950).

Law of the Badlands (1951) was the cheapest Tim Holt vehicle since the war years, made for $98,000, but still recorded a loss of $20,000.

[46] After Gunplay (1951), Saddle Legion (1951) had a higher quality female lead – Dorothy Malone – and then Holt unexpectedly appeared in an "A", supporting Robert Mitchum and Jane Russell in His Kind of Woman for director John Farrow.

In September 1950 it was announced Holt would support Montgomery Clift for director Nicholas Ray in The Flying Leathernecks (1951) but the film was made without either actor.

[47] Instead it was back to Westerns: Pistol Harvest (1951), Hot Lead (1951), Overland Telegraph (1951), Trail Guide (1952), Road Agent (1952), Target (1952), and finally Desert Passage (1952).

[22] He was absent from the screen for five years until he starred in a horror film, The Monster That Challenged the World, in 1957, Holt said it "wasn’t too bad a picture at all".

Tim Holt died from bone cancer on February 15, 1973,[48] in Shawnee, Oklahoma, where he had been managing a radio station.