Marianne Steinbrecher, known as Mari (born August 23, 1983), is a volleyball player from Brazil, who plays as a wing spiker (basically outside hitter, occasionally opposite hitter) at Molico/Osasco. She represented her native country at the 2008 Summer Olympics in Beijing, China, in which she helped her country win the gold medal. She is known for her high arm swing when hitting and her ability to hit over the top of most blocks.
Born in São Paulo, Steinbrecher, who is of Russian and German descent, started playing volleyball when she was 14 years old. After playing for Rolândia/Faccar and Grêmio Londrinense, she professionalized while playing for Osasco. Playing for Osasco, she won the Salonpas Cup in 2001, in 2002 and in 2005, the Campeonato Paulista in 2003, and the Superliga in 2003–04. In 2006, she left Osasco and joined Italian club Scavolini Pesaro. In 2008, she returned to Brazil to play for São Caetano/Blausiegel in the Copa Brasil. In 2010 she signed a contract with the Brazilian club Unilever Volley. She played with Fenerbahçe in the 2012 FIVB Club World Championship held in Doha, Qatar and helped her team to win the bronze medal after defeating Puerto Rico's Lancheras de Cataño 3-0.
Playing for the national team, she won the FIVB World Grand Prix in 2004, in 2006, in 2008 and in 2009. In the 2008 FIVB World Grand Prix, she was awarded the competition's Most Valuable Player (MVP). Steinbrecher participated in the 2004 Summer Olympics, in which her country finished in the fourth place, after being defeated by Cuba in the bronze medal match. In the 2007 Pan American Games, she won the silver medal, after her country was defeated by Cuba in the final. In 2008, Steinbrecher helped Brazil win the FIVB World Grand Prix, also winning the competition's Most Valuable Player award. In the same year, on her birthday, in Beijing, Steinbrecher won her first gold medal in the Olympic Games, after her country beat the United States 3–1 in the gold medal match.