His first stories, for Argentine editors such as Colomba and Record, were largely inspired by Hugo Pratt (during the years he spent in Argentina) and Francisco Solano Lopez. Back to Spain, he worked for Spanish (Zona 84, Comix International) and Italian (Lanciostory, Skorpio) magazines. His work of this period is mainly related to war and science-fiction genres.
In the 1980s he collaborated with several European magazines, including the Spanish 1984, the French Metal Hurlant and the Italian L'Eternauta, experimenting with graphical and narrative innovations. To this period dates what is ranked among his best series, the short science-fictions stories known under the title of Time Paradox. Also noteworthy are The City, written by Ricardo Barreiro and Le Quatrième Pouvoir - (The Fourth Power), which he wrote by himself.
Giménez's style has become famous for the extreme attention he devotes to technical and historical details; his series Pik As has been defined as a comic encyclopaedia of World War II Otherwise, his human figures are often standard and drawn without special characteristics.
Giménez also collaborated with important authors such as Carlos Trillo, Emilio Balcarce, Roberto Dal Prà, and Chilean Alejandro Jodorowsky, with whom he authored the popular Metabarons saga started in 1992.