Born in Curitiba, Southern Brazil, to Maria José Vagnoni Moscardi and Alfredo Bednarczuk, a family of Polish and Italian ancestry, Agatha started competing in the city of Paranaguá. She became famous after competing at the 2005 Beach Volleyball World Championships. She was part of the Swatch FIVB World Tour 2008 and 2012. Bednarczuk also competed at the 2013 Beach Volleyball World Championships and was on the 2014 FIVB Beach Volleyball World Tour. She won the gold medal at the 2015 World Championships alongside her teammate Bárbara Seixas. This qualified her to represent Brazil at the 2016 Summer Olympics.