He debuted as actor in a local 1943 theatre production, El hombre más lindo del mundo (The Best-Looking Manitoba in the World), and in Uruguayan film in a comedy, Detective a contramano (The Detective Goes the Wrong Way, 1949). Given third billing in Spanish director Alberto De Zavalia"s El otro yo de Marcela (1950). He later joined Argentine latin jazz drummer Tito Alberti as a vocalist in Alberti"s Jazz Casino Orchestra, touring throughout Latin America until 1957.
Mareco eventually relocated to Spain in 1962.
Nicknamed Pinocho (Pinocchio), he was cast by that stage name in a number of Spanish comedies during the 1950s and "60s, and was both the Spanish language voice actor and the foil for the South American version of Italian marionette Topo Gigio. Settling in Argentina, he earned four Martín Fierro Awards from 1967 to 1972, but after 1976, faced political persecution in Argentina because of his Peronist sympathies.
He returned to Argentine television after the 1982 Falklands War as host of a successful, no-frills afternoon talk show, Cordialmente. Juan Carlos Mareco died on October 8, 2009 aged 83.
His remains are buried at Cementerio Parque Jardín de Paz, in Pilar.