Born at Vercelli, he started his career with an amateur team, Belvedere in 1990–91, and made his debut at the professional level at the age of 17 for A.S. Casale Calcio. The following year Mero signed for Parma F.C., playing with the Primavera team before being sold to Crevalcore, with whom he won the Serie C2 league. In 1995, he was signed by Ravenna, team for which he played three seasons, obtaining a promotion to Serie B. He moved to Brescia in 1998, obtaining his first promotion to Serie A and making his European debut as team captain in the 2001 UEFA Intertoto Cup, in which Brescia reached the finals, eventually losing to Paris Saint-Germain. During his time there, he was nicknamed Sceriffo (Sheriff) by his coach Nedo Sonetti for his diligence and reliability.