His father wanted him to become a soldier but he ran away from a military academy aged 17 and began his career as a page boy for Sarah Bernhardt's company.
[3] In 1924, he joined Paramount Theatres Limited, building up its circuit and opening the Plaza and Carlton cinemas.
Their films included Hamlet, Fame is the Spur, Uncle Silas, The October Man, Vice Versa, The Mark of Cain and One Night with You.
In 1948 he was appointed Executive Producer at the studios by Rank's Managing Director John Davis with a brief to rein in financial losses.
The Woman in Question (1950) was a thriller with Kent and Dirk Bogarde, and Highly Dangerous (1950) was an unsuccessful attempt to restore Margaret Lockwood to her mid 1940s popularity.
The latter was based on a play by Terence Rattigan and St. John would go on to approve a number of films based on plays: "I started out as manager of a small out-of-town cinema, and I viewed films from the out-of-London angle," he explained in 1951; "This experience made me realise that the ordinary people in the remotest places in the country were entitled to see the works of the best modern British playwrights.
"[10] The film was directed by Anthony Asquith, and St. John promptly agreed to finance another play adaptation from that director, The Importance of Being Earnest (1952), which was popular.
Also popular was Encore (1951) based on the stories of W. Somerset Maugham, Venetian Bird (1952), a thriller from the director-producer team of Ralph Thomas and Betty E. Box who would become crucial to Rank, and The Card (1952) with Alec Guinness.
St. John decided to finance an action drama set during the Malayan Emergency, The Planter's Wife (1952), directed by Ken Annakin and starring Jack Hawkins and Anthony Steel.
St. John commissioned a number of thrillers at Rank, including: Hunted (1952), and Desperate Moment (1953), both with Dirk Bogarde; The Long Memory (1953) with John Mills; The Net (1953); Turn the Key Softly (1953); The Kidnappers (1953); Forbidden Cargo (1954); Passage Home (1955); Lost (1956); and House of Secrets (1956).
In the early 1950s, St. John moved Rank more into the comedy area with films such as: Made in Heaven (1952); Penny Princess (1953) with Bogarde; Always a Bride (1953); and A Day to Remember (1953).
[12] St. John spotted Norman Wisdom on television in a Christmas Party special, signed him to a seven year contract and starred him in Trouble in Store (1953), which was a huge success.
Later comedies with Sinden included :You Know What Sailors Are (1954); Mad About Men (1954); The Beachcomber (1954) with Robert Newton; To Paris with Love (1955) with Guinness; All for Mary (1955); Value for Money (1955) with Gregson and Diana Dors; Simon and Laura (1955) with Peter Finch and Kendall; An Alligator Named Daisy (1955), with Donald Sinden and Dors again; and Jumping for Joy (1956) with Frankie Howerd.
Pinewood Studios' quota of 15 films a year, for which St. John is responsible and which average £150,000 each, is the largest in Britain today.
In the past four years he has supervised the making of more than 50 films... St. John has earned a reputation for being a driving showman with a gift for succinct expression.
[15] In the late 1950s St. John financed a series of adventure films shot on location overseas in colour based on some best-selling novel.
"[17] Anthony Havelock-Allan said "he did what [Rank chairman John] Davis told him to... nice man but not creative at all, not imaginative.
"[19] Frank Godwin, who worked with St John as assistant executive producer, called him "A lovely, charming man, a very warm hearted character and, above all, a great showman.
[24] He called him: That enigmatic quasi-Englishman who convinced most strangers that he was a distinguished member of the aristocracy, whereas his apparent title sprang from the same line as Duke Ellington and King Vidor.
Frequently out of favour with the higher echelons, he stepped into the wings on several occasions to allow more flashy luminaries to occupy the stage.
[11]: 42–43 St. John retired in 1964, after The High Bright Sun (1964), the last collaboration between Ralph Thomas, Betty Box and Dirk Bogarde.