The young defender's contract has been extended until the summer of 2013 as he has been promoted to the senior team ahead of the new season
The 21-year-old defender was a regular in the Barcelona B squad that finished third in the Segunda Division last season, and was temporarily included in first team affairs in March to provide cover for Eric Abidal, who had been diagnosed with a liver tumour.
Fontas continued working with the senior side until the end of the season and appeared in eight games in total.
The Spain under-21 starlet, who made his first team debut in the 2009-10 league campaign against Sporting Gijon at Camp Nou, joined the club from Girona in 2007, playing in the youth team for a season and for Barcelona B for two-and-a-half years before moving up to the first team.
Fontas' contract has automatically been extended until the summer of 2013 following his new role, and his buy-out clause has been raised to €30 million.