The name Marcelo has its roots in ancient Rome and is derived from the Latin name Marcus, which means "dedicated to Mars," the Roman god of war. The name Marcus was a common Roman praenomen, or personal name, during the Roman Republic and Empire.

Marcelo is the Spanish and Portuguese diminutive form of Marcus, with the added "-elo" suffix. This diminutive form was likely popularized during the Middle Ages in the Iberian Peninsula, where Latin names were adapted and Romanized forms flourished.

One of the earliest recorded instances of the name Marcelo can be found in the 6th century, when a Visigothic nobleman named Marcelo served as the governor of the city of Mérida in modern-day Spain. During the Middle Ages, the name Marcelo was relatively common among the nobility and clergy in Spain and Portugal.

In the 16th century, Marcelo Cervino (1501-1555) was an Italian cardinal who served as the Dean of the College of Cardinals and was a prominent figure during the Council of Trent, a crucial event in the Catholic Counter-Reformation.

Another notable figure who bore the name Marcelo was the 17th-century Portuguese painter Marcelo Ramos (1612-1693), who was known for his religious works and portraits of the Portuguese nobility.

In the 19th century, Marcelo Gomes da Silva (1806-1869) was a Brazilian politician and military leader who played a significant role in the Paraguayan War, also known as the War of the Triple Alliance.

The name Marcelo gained further prominence in the 20th century with individuals like Marcelo Caetano (1906-1980), a Portuguese politician who served as the last Prime Minister of Portugal during the Estado Novo regime from 1968 to 1974.

Additionally, Marcelo Álvarez (born 1962) is an Argentine operatic tenor who has performed in some of the world's most prestigious opera houses, and Marcelo Bielsa (born 1955) is an Argentine professional football manager who is widely regarded as one of the most influential coaches in modern football.