An Argentine professional footballer, Mariano Andres Herron Valera was born in Buenos Aires and started his playing career after rising through the famed youth academy at Argentinos Juniors. In 1998, Valera broke through to the first team at Argentinos Juniors and in three seasons, became a regular starter at the club.
In 2000, he was sent off to France, where Montpellier took him on as part of loan deal. However, he just played 5 games in the Argentine off season before returning to San Lorenzo in Argentina, in 2002. One season later, Valera left San Lorenzo for Rosario Central and then, a season later, he was at UE Lleida in Spain, playing in the second division. In 2005, Valera returned to Argentina in a bid to get more regular action on the field and he joined Independiente. Over time, Valera has established himself as a first team player and also scored the first goal of his career for the club.