Ammann made his debut as a 16-year-old rookie during the 1997–1998 Ski jumping World Cup season. Ammann qualified for the 1998 Olympic Games in Nagano, Japan, where he finished 35th.
Prior to the 2002 Winter Olympics in Salt Lake City, Ammann crashed and suffered injuries during training in Willingen. Despite this, he won a gold medal in both the undividual normal hill and large hill competitions, being only the second athlete to accomplish this feat (Matti Nykänen having done so in 1988). Following the Olympics, Ammann became a star in Switzerland and also made appearances on American talk shows, such as the Late Show with David Letterman (on 20 February 2002).
Ammann also won the ski jumping event at the Holmenkollen Ski Festival in 2002 and 2007. This earned him the Holmenkollen medal in 2007 (shared with Frode Estil, Odd-Bjørn Hjelmeset, King Harald V, and Queen Sonja of Norway).
He made his third Olympic appearance in 2006 in Turin, Italy.
On 24 February 2007, he won his first medal at the FIS Nordic World Ski Championships with a victory in the Individual Large Hill in Sapporo, Japan. Ammann would follow this with a silver medal in the Individual Normal Hill the following week. Ammann would complete his set of medals with a bronze medal in the Individual Normal Hill event at the FIS Nordic World Ski Championships 2009 in Liberec, Czech Republic.
In 2010, competing in his fourth Olympics in Vancouver, British Columbia, Canada, Ammann won the gold medal in the Individual Normal Hill event. He became the first man in Olympic history to win gold medals in the Individual Normal Hill event in two Olympics.
On 20 February 2010, he also won a gold medal in the Individual Large Hill event at the Winter Olympics in Vancouver, thus becoming the first man to win gold medals in both individual ski jumping events in two Olympic games, as well as the most decorated Swiss Olympic athlete of all time. His first jump was 144 meters. His second jump was 138 meters.
In March 2010, Ammann became the overall winner of 2009–10 FIS Ski Jumping World Cup, winning all four events at the Nordic Tournament and nine World Cup events in one season overall. He finished the season by becoming the ski flying World Champion in Planica on the largest hill in the world. His 236.5 m fourth round jump was the longest jump of the event and then the second longest jump in history.
He won his most recent gold medal on the FIS World Cup circuit in December 2013. He was selected flag-bearer of the Swiss Winter Olympics team at Sochi, Russia, in February 2014.
The 2014 Winter Olympics in Sochi were disappointing for Ammann. He called a news conference, and there was a lot of buzz that he was going to announce his retirement. However, he merely gave a long talk about how it was too early to decide.
On 6 January 2015, Ammann was injured on his second-round jump in Bischofshofen during the final stage of the 2014/15 Four Hills Tournament. His representation has since stated that his condition is stable, with the most damage being to his face. The Four Hills tournament proved to be a very tough outing overall for Ammann, as he also fell in the first round in Oberstdorf.
Simon Ammann was born in Grabs, Switzerland, to Margit and Heinrich Ammann and raised in Unterwasser, Switzerland. He has two brothers and three sisters. He married Yana Yanovskaya on 25 June 2010. Ammann is a student of information technology and electrical engineering at ETH Zurich since 2006. Ammann currently lives in Schindellegi, Switzerland. In October 2014 his wife gave birth to their son Théodore. On January 17, 2017 his daughter Charlotte was born.