Conrado San Martín left behind a career as an amateur boxer to take small roles in the theater in the company of Cayetano Luca de Tena and to act as an extra in some films.
These roles led the Catalan production company Emisora films to give him an exclusive contract and he starred in the comedies: Siempre vuelve de madrugada (1948) (He always come back at dawn): Despertó su corazón Awoke his heart (1949) and Mi adorado Juan My beloved Juan (1949) a film directed by Jerónimo Mihura.
[2] San Martín also took roles in the thriller Apartado de correos 1001 (1950); Mail box 1001, a film directed by Julio Salvador which was a great hit with audiences; and Relato policíaco (1954) by Antonio Isasi-Isasmendi.
The success of some of these productions gave him the starring role in Amenaza (1950); Threat a film directed by Antonio Román; La patrulla, (1954) a film directed by Pedro Lazaga with Carmen Sánchez and Arturo Fernández; Pasión en el mar (1956) and o ...Y eligió el infierno (1957).
He created his own production company, Laurus films, producing the melodramas: Lo que nunca muere (1954) and Sin la sonrisa de Dios (1955).