He started swimming at the instigation of his grandfather, who was a swimming teacher, at the age of two years. He tried judo at 10 years old, but left due to his mother. His first club was the Canto do Rio in Niterói. At age 13, he moved to Fluminense. Three years later, he moved to Vasco, where he stayed until 2000. He participated at the 1999 Pan American Games in Winnipeg, where he finished 11th in the 100-metre butterfly, and 11th in the 200-metre individual medley. He was at the 2003 World Aquatics Championships in Barcelona, where he finished 37th in the 100-metre butterfly. Prior to the 2004 Olympics, he came to the United States, where he was trained by the Olympic champion Anthony Nesty. At the 2004 Summer Olympics, Mangabeira made it to the finals of the 100-metre butterfly where he finished in sixth place, beating the South American record, and swimming alongside well-known swimmers like Ian Crocker and Michael Phelps. Mangabeira was a semifinalist at the 2005 World Aquatics Championships in Montreal, in the 100-metre butterfly, where he finished in 13th place, and in the 50-metre backstroke, where he came in at 16th place. He was at the 2006 FINA World Swimming Championships in Shanghai, where he finished 19th in the 100-metre butterfly, 20th in the 50-metre backstroke and 9th in the 4×100-metre medley. He swam at the 2006 Pan Pacific Swimming Championships, where he finished 5th in the 100-metre butterfly and 7th in the 4×100-metre medley. Mangabeira also qualified to compete in the 2007 World Aquatics Championships in the 100-metre butterfly and 50-metre backstroke, but did not make it past the initial heats. He ranked 17th in the 100-metre butterfly and 9th in the 4×100-metre medley, helping the Brazilian relay to qualify for the 2008 Olympics. At the 2007 Pan American Games in Rio de Janeiro, he won the silver medal in the 100-metre butterfly, and also helped the Brazilian 4×100-metre medley relay in heats, winning the silver medal in the event. Mangabeira returned to the Olympics in 2008 to compete in the 100-metre butterfly, but did not advance beyond the first heats. He finished 23rd. In 2009, Mangabeira competed in the 2009 World Aquatics Championships in the 100-metre butterfly and 4×100-metre medley relay, and reached the finals in both events, finishing eighth in the individual race and fourth in the relay, which he swam with Guilherme Guido, Henrique Barbosa and César Cielo Filho. He swam the butterfly leg for the Brazilian medley relay team, in a race where the first 4 relays beat the U.S. world record from Beijing 2008. At the 2010 South American Games in Medellín, Mangabeira won a gold medal in the 4×100-metre medley. He was at the 2010 Pan Pacific Swimming Championships in Irvine, where he finished 4th in the 4×100-metre medley, 15th in the 100-metre butterfly, and 15th in the 100-metre backstroke. At the 2011 Pan American Games in Guadalajara, Mangabeira won gold in the 4×100-metre medley and in the 4×100-metre freestyle.
