Young Prince Karl (Edmund Purdom), of a small sub-kingdom of the German Empire, is sent off near the turn of the 20th century to get a university education in Heidelberg, Baden-Wuerttemberg. His grandfather (Louis Calhern) was one of a handful of petty kings within German-speaking central Europe. Fictional Karlsburg is small, but fiercely proud of its history and traditions.
Karl has been raised most of his life for the military, but when it comes time for him to marry, the princess (Betta St. John) picked for him cannot stand his stiff formality. This would not be such a problem but for the fact that Karlsburg has no great wealth, only good breeding. His tutor recommends that he be sent to university to develop an easier, more sociable manner.
He (eventually) slips into the social mix, becomes accepted as a "good chap" by his student peers, and falls deeply in love with Kathie (Ann Blyth), a pretty, popular, and musically inclined barmaid, who holds "court" in the local biergarten. Love notwithstanding, when his old grandfather dies unexpectedly, the young prince must marry the princess and take his place in the small kingdom that he is destined to rule. He returns for one last time to Heidelberg to bid Kathie a poignant farewell.
The parallel subplot of the princess being in love with Count Tarnitz, whom she cannot marry, was completely omitted from the film.
It featured, as the credits read, "the singing voice of Mario Lanza". Lanza had become embroiled in a bitter dispute with Metro-Goldwyn-Mayer during production and the studio fired him. However, some sources state that Lanza had voluntarily walked off the picture. Under the terms of the settlement with Lanza, MGM retained the film rights to the soundtrack that Lanza had already recorded. The songs from this film (including "Beloved" – written specially for the movie – and the well-remembered "Serenade", from the original show) would become some of those most identified with Lanza, even though they were mouthed in the film by Edmund Purdom, who took over the role of Prince Karl. Ann Blyth starred as Kathie. Blyth had played opposite Lanza in the 1951 blockbuster The Great Caruso.
The film also featured John Ericson, Louis Calhern, Edmund Gwenn, S.Z. Sakall, Betta St. John, John Williams, Evelyn Varden and John Hoyt.
The film was directed by Richard Thorpe (who replaced the original director, Curtis Bernhardt) and produced by Joe Pasternak. The screenplay was by Sonya Levien and William Ludwig and was based on the operetta The Student Prince by Sigmund Romberg and Dorothy Donnelly which was in turn based on the 1901 play Old Heidelberg by Wilhelm Meyer-Förster. New scenes and rewritten dialogue not found in the stage production were also added, although the basic plot remained the same. Additional songs were specially written by Nicholas Brodszky and Paul Francis Webster. Many of Ms. Donnelly's original stage lyrics were completely changed for the film. Owing to the story's popularity it has been turned into films on numerous occasions, including the American silent film Old Heidelberg (1915), the German silent film Old Heidelberg (1923), Ernst Lubitsch's The Student Prince in Old Heidelberg (1927), and Ernst Marischka's Old Heidelberg (1959).
The film was a big hit - according to MGM records it made $2,528,000 in the US and Canada and $2,813,000 in other countries, resulting in a profit of $451,000.
Lanza made two recordings of the songs from the movie – the first was a genuine film soundtrack recording, in mono. In 1959, after stereo had become possible on records, another recording with Lanza was issued. But rather than simply reissuing the original soundtrack in stereo (which would have been possible since the movie was filmed using 4-track stereo, and stereo albums were released starting in 1958), RCA Victor recorded an all-new studio cast album of the score, and the role of Kathie was sung by soprano Norma Giusti. The original Dorothy Donnelly lyrics were restored to this album. Both the 1954 and 1959 albums, however, also included the three additional songs written specially for the film version ("Summertime in Heidelberg," "I'll Walk With God," and "Beloved"), and both albums omit the solo for Kathie, "Come Boys".