He began his career with Racing Club and Estudiantes before joining River Plate in 2012, going on to win six domestic and international tournaments including the 2015 Copa Libertadores.

Born in Puerto Madryn, Chubut, Mercado made his professional debut for Racing Club on 21 February 2007 in a 0–1 home defeat to San Lorenzo.

[7] Mercado represented the Argentina Under-20 team at the 2007 South American Youth Championship in Paraguay and at the 2007 FIFA U-20 World Cup in Canada.

Mercado made his full international debut for the Argentina national team after being called up to join Diego Maradona's squad of Argentina-based players who beat Jamaica 2–1 on 10 February 2010.

Mercado was first-choice in his position for Argentina in the 2016 Copa América Centenario squad, playing in the final against Chile for the full 120-minutes, a 4–2 loss on penalties.