Naish's uncredited bit role in What Price Glory? (
1926) launched his career in more than two hundred films.
He was twice nominated for an Academy Award for Best Supporting Actor, the first for his role as Giuseppe in the movie Sahara (1943) in which he delivers one of the most moving speeches in any wartime film: 
Mussolini is not so clever like Hitler, he can dress up his Italians only to look like thieves, cheats, murderers, he cannot like Hitler make them feel like that.
He cannot like Hitler scrape from their conscience the knowledge right is right and wrong is wrong, or dig holes in their heads to plant his own Ten Commandments- Steal from thy neighbor, Cheat thy neighbor, Kill thy neighbor!
But are my eyes blind that I must fall to my knees to worship a maniac who has made of my country a concentration camp, who has made of my people slaves?
Must I kiss the hand that beats me, lick the boot that kicks me?
NO!

 The second was for his performance as the title character's Hispanic father in the movie A Medal for Benny (1945).
For the latter film, he won the Golden Globe Award for Best Supporting Actor – Motion Picture.

He often played villains from gangsters in numerous Paramount pictures to mad scientists, such as Dr. Daka in the Batman film serial.
In the 1940s Naish was a supporting character in a number of horror films.
He played Boris Karloff's assistant in House of Frankenstein (1944).

Of Irish descent, he rarely played an Irishman, explaining, "When the part of an Irishman comes along, nobody ever thinks of me."
He portrayed numerous other ethnicities including Southern European, Eastern European, Latin American, Native American, Middle Eastern, South Asian, East Asian, Southeast Asian, Pacific Islander—even African American, which earned him the moniker "Hollywood's one-man U.N.".

On radio, Naish starred as Luigi Basco on the popular CBS program Life with Luigi (1948–1953).
Luigi's popularity resulted in a CBS television series of the same name, with Naish reprising his role.

In 1955, Naish originated the role of Alfieri in the one-act, verse version of Arthur Miller's A View from the Bridge on Broadway, also starring Van Heflin and Eileen Heckart.

In 1971, he appeared in his final film role, Dracula vs. Frankenstein (1971), as a mad scientist; a role descended from the original Dr. Frankenstein takes to murdering young women for experimentation in hopes of reviving his ancestor's creation, with help from his mute assistant, played by Lon Chaney Jr., whose film appearance was also his last.
Naish's uncredited bit role in What Price Glory? (1926) launched his career in more than two hundred films. He was twice nominated for an Academy Award for Best Supporting Actor, the first for his role as Giuseppe in the movie Sahara (1943) in which he delivers one of the most moving speeches in any wartime film: 
Mussolini is not so clever like Hitler, he can dress up his Italians only to look like thieves, cheats, murderers, he cannot like Hitler make them feel like that. He cannot like Hitler scrape from their conscience the knowledge right is right and wrong is wrong, or dig holes in their heads to plant his own Ten Commandments- Steal from thy neighbor, Cheat thy neighbor, Kill thy neighbor! But are my eyes blind that I must fall to my knees to worship a maniac who has made of my country a concentration camp, who has made of my people slaves? Must I kiss the hand that beats me, lick the boot that kicks me? NO!
 The second was for his performance as the title character's Hispanic father in the movie A Medal for Benny (1945). For the latter film, he won the Golden Globe Award for Best Supporting Actor – Motion Picture.
He often played villains from gangsters in numerous Paramount pictures to mad scientists, such as Dr. Daka in the Batman film serial. In the 1940s Naish was a supporting character in a number of horror films. He played Boris Karloff's assistant in House of Frankenstein (1944).
Of Irish descent, he rarely played an Irishman, explaining, "When the part of an Irishman comes along, nobody ever thinks of me." He portrayed numerous other ethnicities including Southern European, Eastern European, Latin American, Native American, Middle Eastern, South Asian, East Asian, Southeast Asian, Pacific Islander—even African American, which earned him the moniker "Hollywood's one-man U.N.".
On radio, Naish starred as Luigi Basco on the popular CBS program Life with Luigi (1948–1953). Luigi's popularity resulted in a CBS television series of the same name, with Naish reprising his role.
In 1955, Naish originated the role of Alfieri in the one-act, verse version of Arthur Miller's A View from the Bridge on Broadway, also starring Van Heflin and Eileen Heckart.
In 1971, he appeared in his final film role, Dracula vs. Frankenstein (1971), as a mad scientist; a role descended from the original Dr. Frankenstein takes to murdering young women for experimentation in hopes of reviving his ancestor's creation, with help from his mute assistant, played by Lon Chaney Jr., whose film appearance was also his last.
J. Carrol Naish