The 46-year-old businessman will replace Joan Laporta, who steps down at the end of the month, after gaining 61.35 percent of the vote against three other candidates Agusti Benedito, Marc Ingla and Jaume Ferrer.
Rosell collected 35,021 votes, the highest in the club's history after a record turnout, as Barca's 'socios' (club members) failed to rally behind Laporta's preferred successor Ferrer, who came in last.
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"I will be a president for everyone. I know it's a position with a great deal of responsibility. I will not fail you," Rosell told a news conference.
Rosell has won favour despite Laporta having presided over one of the club's most successful periods since he took the helm in 2003, during which time they won two European Cups, four La Liga titles and a King's Cup.
Rosell was the favourite from the outset and distanced himself from the current management, having resigned from the club in 2005 after two years as vice-president for sport.
During his time, he was credited with bringing Deco and Ronaldinho to Barca before quitting over disagreements with Laporta.
Rosell runs his own sports marketing business, which he has said he will step down from, and in the past was a marketing director for Nike in Spain and Portugal.
There was little difference between the four presidential candidates over the running of the sporting side of the club after a hugely successful couple of years.
Rosell has said he would offer coach Pep Guardiola a six-year contract and that he would like to turn him in to Barcelona's Alex Ferguson.
He has said he would look to replace Txiki Begiristain as sports director and that he would renovate the Nou Camp, but scrap the plans drawn up under Laporta with the architect Norman Foster.
All candidates were in favour of pursuing Arsenal's Spain midfielder Cesc Fabregas, though Rosell had warned that he would not do so at any cost.
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