While studying drama at Los Angeles City College, Mitchell was introduced to modern dance at the school of the famed teacher and choreographer, Lester Horton.
After receiving his associate degree, he joined Horton's company, where he remained for nearly four years.
While working with Horton, he became a close friend of dancer Bella Lewitzky; in the 1970s, he became President of the Board of Directors of her Dance Foundation, and afterwards remained a "major longtime […] supporter" of hers.
In 1944, Horton took Mitchell to New York with him to form a new dance company, but the venture abruptly collapsed.

As it happened, the failure of Horton's company was a significant turning point in Mitchell's career: while struggling to find either acting or dancing roles in New York, he successfully auditioned for Agnes de Mille, who was choreographing her first musical since Oklahoma!.
Mitchell, who did not study ballet until he was in his mid-twenties, was at a loss when faced with de Mille's ballet combination.
Much later, describing his approach to the audition, he said, "Well, I really hadn't too much familiarity with that but I threw myself across the floor and about the third or fourth pass, Agnes cried 'Stop' and summoned me over and said 'Where on earth did you get your dance training?'".
De Mille nevertheless offered him the dual position of principal dancer and assistant choreographer.
 Given the option between touring with Helen Hayes and dancing for de Mille, he chose de Mille.

Bloomer Girl (1944) began an important artistic partnership with de Mille that lasted from 1944 to 1969 and spanned theater, film, television, and concert dance.
De Mille's biographer, Carol Easton, describes him as the "quintessential male de Mille dancer" and de Mille's "closest confidant" in her artistic life.
In one of her autobiographical volumes, de Mille herself said of Mitchell that he had "probably the strongest arms in the business, and the adagio style developed by him and his partners has become since a valued addition to ballet vocabulary."

When, nearly thirty years later, an interviewer asked Mitchell to respond to de Mille's comments, he offered a more modest assessment of his career: "I was primarily an actor [...] and I think what Agnes was referring to was my acting and regard for the woman I was partnering.
Because in the end I really was a partner.
 When I look at today's dancers, or I look at the great dance films, such as Seven Brides for Seven Brothers--I couldn't do any of that!
I know I was a dancer, but I didn't have the technique.
 At most I was an actor-dancer."

Mitchell's work with de Mille:
Bloomer Girl (Broadway, 1944): principal male dancer; assistant choreographer
Brigadoon (Broadway, 1947): Harry Beaton; assistant choreographer
Paint Your Wagon (Broadway, 1951): Pete Billings; assistant choreographer
Come Summer (Broadway, 1969): assistant director
American Ballet Theatre (1950–51, 1955, 1956): Rodeo (Head Wrangler — ABT premiere cast), Fall River Legend (Pastor), Rib of Eve (Husband — world premiere cast)
Agnes de Mille Dance Theatre (1953–54): principal dancer
Royal Winnipeg Ballet (1964): Bitter Weird (Bridegroom)
Oklahoma! (
film, 1955): Dream Curly (excerpted in That's Dancing!)

Omnibus (TV, 1956): featured dancer, "Art of Ballet"; featured dancer, "Art of Choreography"
Bloomer Girl (TV, 1956): The Returned Soldier
Gold Rush (TV, 1958): Miner
Mitchell's other close associations were with Gower Champion, Eugene Loring (with whom he also trained), and Jerome Robbins:
Gower Champion:
Carnival! (
Broadway, 1961; national tour, 1962; West End, 1963): Marco the Magnificent
Mack & Mabel (Broadway, 1974): William Desmond Taylor
Annie Get Your Gun (tour, 1977): assistant director
Eugene Loring:
The Toast of New Orleans (film, 1950): Pierre — "The Tina-Lina" with Rita Moreno
Deep in My Heart (film, 1954): Specialty dancer — "One Alone" with Cyd Charisse
Ford Startime: Meet Cyd Charisse (TV, 1959): Partnered Cyd Charisse
The Perry Como Show (TV, 1963): Partnered Cyd Charisse
The 38th Academy Awards (TV, 1966): Partnered C
While studying drama at Los Angeles City College, Mitchell was introduced to modern dance at the school of the famed teacher and choreographer, Lester Horton. After receiving his associate degree, he joined Horton's company, where he remained for nearly four years. While working with Horton, he became a close friend of dancer Bella Lewitzky; in the 1970s, he became President of the Board of Directors of her Dance Foundation, and afterwards remained a "major longtime […] supporter" of hers. In 1944, Horton took Mitchell to New York with him to form a new dance company, but the venture abruptly collapsed.
As it happened, the failure of Horton's company was a significant turning point in Mitchell's career: while struggling to find either acting or dancing roles in New York, he successfully auditioned for Agnes de Mille, who was choreographing her first musical since Oklahoma!. Mitchell, who did not study ballet until he was in his mid-twenties, was at a loss when faced with de Mille's ballet combination. Much later, describing his approach to the audition, he said, "Well, I really hadn't too much familiarity with that but I threw myself across the floor and about the third or fourth pass, Agnes cried 'Stop' and summoned me over and said 'Where on earth did you get your dance training?'". De Mille nevertheless offered him the dual position of principal dancer and assistant choreographer.  Given the option between touring with Helen Hayes and dancing for de Mille, he chose de Mille.
Bloomer Girl (1944) began an important artistic partnership with de Mille that lasted from 1944 to 1969 and spanned theater, film, television, and concert dance. De Mille's biographer, Carol Easton, describes him as the "quintessential male de Mille dancer" and de Mille's "closest confidant" in her artistic life. In one of her autobiographical volumes, de Mille herself said of Mitchell that he had "probably the strongest arms in the business, and the adagio style developed by him and his partners has become since a valued addition to ballet vocabulary."
When, nearly thirty years later, an interviewer asked Mitchell to respond to de Mille's comments, he offered a more modest assessment of his career: "I was primarily an actor [...] and I think what Agnes was referring to was my acting and regard for the woman I was partnering. Because in the end I really was a partner.  When I look at today's dancers, or I look at the great dance films, such as Seven Brides for Seven Brothers--I couldn't do any of that! I know I was a dancer, but I didn't have the technique.  At most I was an actor-dancer."
Mitchell's work with de Mille:
Bloomer Girl (Broadway, 1944): principal male dancer; assistant choreographer
Brigadoon (Broadway, 1947): Harry Beaton; assistant choreographer
Paint Your Wagon (Broadway, 1951): Pete Billings; assistant choreographer
Come Summer (Broadway, 1969): assistant director
American Ballet Theatre (1950–51, 1955, 1956): Rodeo (Head Wrangler — ABT premiere cast), Fall River Legend (Pastor), Rib of Eve (Husband — world premiere cast)
Agnes de Mille Dance Theatre (1953–54): principal dancer
Royal Winnipeg Ballet (1964): Bitter Weird (Bridegroom)
Oklahoma! (film, 1955): Dream Curly (excerpted in That's Dancing!)
Omnibus (TV, 1956): featured dancer, "Art of Ballet"; featured dancer, "Art of Choreography"
Bloomer Girl (TV, 1956): The Returned Soldier
Gold Rush (TV, 1958): Miner
Mitchell's other close associations were with Gower Champion, Eugene Loring (with whom he also trained), and Jerome Robbins:
Gower Champion:
Carnival! (Broadway, 1961; national tour, 1962; West End, 1963): Marco the Magnificent
Mack & Mabel (Broadway, 1974): William Desmond Taylor
Annie Get Your Gun (tour, 1977): assistant director
Eugene Loring:
The Toast of New Orleans (film, 1950): Pierre — "The Tina-Lina" with Rita Moreno
Deep in My Heart (film, 1954): Specialty dancer — "One Alone" with Cyd Charisse
Ford Startime: Meet Cyd Charisse (TV, 1959): Partnered Cyd Charisse
The Perry Como Show (TV, 1963): Partnered Cyd Charisse
The 38th Academy Awards (TV, 1966): Partnered C
James Mitchell (actor)