Marty played youth ice hockey with the local club, EHC Wettingen-Baden. She made her debut in the SWHL A with SC Zug in the 2003–04 season, at age 15, and played the following two seasons with the team. She began her collegiate career in the 2007–08 season with the New Hampshire Wildcats of Hockey East of the NCAA Division I. As a freshman with the Wildcats, Marty scored 10 points in 32 games and played in the 2008 NCAA Championship quarterfinals. She transferred to Syracuse University for the 2008–09 season and remained with the Syracuse Orange until her graduation in 2011. Marty's twin sister, Julia Marty, in an ice hockey defenceman who currently plays with SC Reinach of the SWHL A. With the exception of their sophomore through senior years in college, Stefanie and Julia played together on the same teams for the entirety of Stefanie’s career.
Swiss national team
Prior to the NCAA, she was nominated to be Swiss Hockey Woman of the Year in 2005. Her Swiss team placed eighth in the 2004 World Championship at Halifax. Marty appeared in the 2006 Olympic games in Torino where her team earned seventh place. From 2003–2007, she played for the EV Zug in the Swiss league. The team earned two Swiss Championships in 2004 and 2005 and two Swiss Vice-Championships in 2006 and 2007. At the Vancouver Winter Games, she tied the Olympic record for most goals scored in a single tournament with nine and helped her homeland to a fifth-place finish. In a game against Russia at the 2012 IIHF Women's World Championship, Stefanie Marty scored two goals in a 5–2 victory, as Switzerland advanced to the semifinals.
Syracuse
During the week of 2 October 2009, Marty accumulated three points in Syracuse's 3–3 tie at Boston College. In addition, she scored a goal in a game against the New Hampshire Wildcats, her former team. Marty was part of all four Syracuse goals in a 4–3 win against Princeton. This occurred during the week of 8 December 2009. She assisted on the game-winning goal. On 1 October 2010, Marty had two goals in a 4–4 tie vs. Northeastern. The Northeastern team featured her twin sister Julia Marty. It was the first time the sisters had played against each other in their NCAA careers.
