Wallach's film debut was in Elia Kazan's controversial 1956 Baby Doll, for which he won the British Academy Film Awards (BAFTA) as "Most Promising Newcomer."
Baby Doll was controversial because of its underlying sexual theme.
Director Elia Kazan however, set explicit limits on Wallach's scenes, telling him not to actually seduce Carroll Baker, but instead to create an unfulfilled erotic tension.
Kazan later explained his reasoning:
What is erotic about sex to me is the seduction, not the act ... The scene on the swing with Eli Wallach and Carroll Baker in Baby Doll is my exact idea of what eroticism in films should be.

Wallach went on to a prolific career as "one of the greatest 'character actors' ever to appear on stage and screen," notes Turner Classic Movies, acting in over 90 films.
Having grown up on the "mean streets" of an Italian American neighborhood, and his versatility as a method actor, Wallach developed the ability to play a wide variety of different roles, although he tried to not get pinned down to any single type of character. "
Right now I'm playing an old man," he said at age 84.
But "I've been through all the ethnic groups, from Mexican bandits to Italian Mafia heads to Okinawans to half-breeds, and now I'm playing old Jews.
Who knows?"

Noting this versatility as a character actor, the Academy of Motion Picture Arts and Sciences called him "the quintessential chameleon," with the ability to play different characters "effortlessly," and L.A. Times theater critic Charles McNulty saw Wallach's "power to illuminate" his various screen or stage personas as being "radioactive."
The Guardian newspaper has written that "Wallach was made for character acting," and includes movie clips from some of his most memorable roles in a tribute to him.

In 1961, Wallach co-starred with Marilyn Monroe, Montgomery Clift and Clark Gable in The Misfits, Monroe's and Gable's last film before their deaths.
Wallach never learned why he was cast in the film, although he suspected that Monroe had something to do with it.
Its screenwriter, Arthur Miller, who was married to Monroe at the time, said that "Eli Wallach is the happiest good actor I've ever known.
He really enjoys the work."

Some of his other films included The Lineup (1958), Lord Jim (1965) with Peter O'Toole, a comic role in How to Steal a Million (1966), again with O'Toole, and Audrey Hepburn, and as Tuco (the 'Ugly') in Sergio Leone's The Good, the Bad and the Ugly (1966) with Clint Eastwood, followed by other Spaghetti Westerns, such as Ace High.
At one point, Henry Fonda had asked Wallach whether he himself should accept a part offered to him to act in a similar Western, Once Upon a Time in the West (1968), which would also be directed by Leone.
Wallach said "Yes, you'll enjoy the challenge," and Fonda later thanked Wallach for that advice.

Wallach and Eastwood became friends during the filming of The Good, the Bad and the Ugly and he recalled their off-work time together: "Clint was the tall, silent type.
He's the kind where you open up and do all the talking.
He smiles and nods and stores it all away in that wonderful calculator of a brain."
In 2003 Wallach acted in Mystic River, produced and directed by Eastwood, who once said "working with Eli Wallach has been one of the great pleasures of my life."

A pivotal moment in Wallach's career came in 1953, when he, along with Frank Sinatra and Harvey Lembeck, tried out for the role of Maggio in the film From Here to Eternity.
Sinatra biographer Kitty Kelly notes that while Sinatra's test was good, it had none of the "consummate acting ability" of Wallach.
Producer Harry Cohn and director Fred Zinnemann were "dazzled" by Wallach's screen test and wanted him to play the part.
However, Wallach had previously been offered an important role in another Tennessee Williams play, Camino Real, to be directed by Elia Kazan, and turned down the movie role.
Wallach said that when he learned that the play had finally received financing, he "grabbed" the opportunity: "It was a remarkable piece of writing by the leading playwright in
Wallach's film debut was in Elia Kazan's controversial 1956 Baby Doll, for which he won the British Academy Film Awards (BAFTA) as "Most Promising Newcomer." Baby Doll was controversial because of its underlying sexual theme. Director Elia Kazan however, set explicit limits on Wallach's scenes, telling him not to actually seduce Carroll Baker, but instead to create an unfulfilled erotic tension. Kazan later explained his reasoning:
What is erotic about sex to me is the seduction, not the act ... The scene on the swing with Eli Wallach and Carroll Baker in Baby Doll is my exact idea of what eroticism in films should be.
Wallach went on to a prolific career as "one of the greatest 'character actors' ever to appear on stage and screen," notes Turner Classic Movies, acting in over 90 films. Having grown up on the "mean streets" of an Italian American neighborhood, and his versatility as a method actor, Wallach developed the ability to play a wide variety of different roles, although he tried to not get pinned down to any single type of character. "Right now I'm playing an old man," he said at age 84. But "I've been through all the ethnic groups, from Mexican bandits to Italian Mafia heads to Okinawans to half-breeds, and now I'm playing old Jews. Who knows?"
Noting this versatility as a character actor, the Academy of Motion Picture Arts and Sciences called him "the quintessential chameleon," with the ability to play different characters "effortlessly," and L.A. Times theater critic Charles McNulty saw Wallach's "power to illuminate" his various screen or stage personas as being "radioactive." The Guardian newspaper has written that "Wallach was made for character acting," and includes movie clips from some of his most memorable roles in a tribute to him.
In 1961, Wallach co-starred with Marilyn Monroe, Montgomery Clift and Clark Gable in The Misfits, Monroe's and Gable's last film before their deaths. Wallach never learned why he was cast in the film, although he suspected that Monroe had something to do with it. Its screenwriter, Arthur Miller, who was married to Monroe at the time, said that "Eli Wallach is the happiest good actor I've ever known. He really enjoys the work."
Some of his other films included The Lineup (1958), Lord Jim (1965) with Peter O'Toole, a comic role in How to Steal a Million (1966), again with O'Toole, and Audrey Hepburn, and as Tuco (the 'Ugly') in Sergio Leone's The Good, the Bad and the Ugly (1966) with Clint Eastwood, followed by other Spaghetti Westerns, such as Ace High. At one point, Henry Fonda had asked Wallach whether he himself should accept a part offered to him to act in a similar Western, Once Upon a Time in the West (1968), which would also be directed by Leone. Wallach said "Yes, you'll enjoy the challenge," and Fonda later thanked Wallach for that advice.
Wallach and Eastwood became friends during the filming of The Good, the Bad and the Ugly and he recalled their off-work time together: "Clint was the tall, silent type. He's the kind where you open up and do all the talking. He smiles and nods and stores it all away in that wonderful calculator of a brain." In 2003 Wallach acted in Mystic River, produced and directed by Eastwood, who once said "working with Eli Wallach has been one of the great pleasures of my life."
A pivotal moment in Wallach's career came in 1953, when he, along with Frank Sinatra and Harvey Lembeck, tried out for the role of Maggio in the film From Here to Eternity. Sinatra biographer Kitty Kelly notes that while Sinatra's test was good, it had none of the "consummate acting ability" of Wallach. Producer Harry Cohn and director Fred Zinnemann were "dazzled" by Wallach's screen test and wanted him to play the part. However, Wallach had previously been offered an important role in another Tennessee Williams play, Camino Real, to be directed by Elia Kazan, and turned down the movie role. Wallach said that when he learned that the play had finally received financing, he "grabbed" the opportunity: "It was a remarkable piece of writing by the leading playwright in 
Eli Wallach