McCormack was born on 7 June 1983 in Helensburgh, New South Wales. She is 168 cm (5 ft 6 in) tall, weighs 73 kilograms (161 lb), is right handed and has a tattoo featuring the Olympic rings.
McCormack entered Helensburgh Public School in 1988 as a kindergartener and later graduated from Kirrawee High School. She began a Bachelor of Primary Education while on scholarship at the New South Wales Institute of Sport (NSWIS). Her partner is a Navy clearance diver.
McCormack was at a barbecue attended by Prince William when he visited Sydney in 2010. At the barbecue, people ".... were surprised by the amount of "royal" attention McCormack, the Australian goalkeeper and a member of the [bronze]-medal winning team at the Beijing Olympics, received especially when Prince William was seen to bow to the amused McCormack at a barbecue."
In 2010, McCormack was working at the New South Wales Institute of Sport as the personal assistant to Charles Turner, the chief executive of the organisation.
McCormack is a goalkeeper, and prefers to wear cap number thirteen. She started playing water polo when she was fourteen years old for the Kirrawee High School team. In 2000, she represented New South Wales on the state junior team. She has a water polo scholarship from the New South Wales Institute of Sport.
McCormack plays her club water polo for the Cronulla Water Polo Club in the National Water Polo League, serving as the team's head coach in 2010 when she was unable to play due to a shoulder injury. She returned to the playing roster in 2011, while also serving as an assistant coach on the team. She continued her involvement with the club into the 2012 season – during which she helped the side to 8–4 and 7–4 wins in the first two games of the season. She took a break from the Cronulla team following their 18 February 2012 game in order to attend the national team training camp.
McCormack is a member of the Australia women's national water polo team and played her first game with the senior team at the 2003 Holiday Cup in the United States. In 2005, she was part of the side that won a bronze medal at the FINA World League Super Finals in Kirishi, Russia. That year, she was also part of the team that finished sixth at the FINA World Championships in Montreal, Canada.
In 2006, McCormack won a gold medal at the Commonwealth Games in Perth, Western Australia. That year, she was also part of the Australian side that finished fourth at the FINA World League Super Finals in Cosenza, Italy. She was also part of the 2006 FINA World Cup team in Tianjin, China, that won a gold medal. In a 2007 Asia-Oceania qualifier for the World League Super Finals, she made seventeen saves in a 19-2 victory against Japan. She was part of the 2007 silver winning side at the FINA World Championship in Melbourne, Australia. She played in goal in the December 2007 series against New Zealand where Australian won the first two tests 18–1 and 17–1.
McCormack was part of Australia's Oceania Olympic qualification campaign in 2008. In an 18–1 victory over New Zealand during the qualifiers, she made twelve saves. She was named to the team that competed in 2008 at the FINA world league preliminary round in Tianjin, China. In a 2008 Asia-Oceania qualifier against China for the World League Super Finals, she played in the 11–9 win that went to a penalty shoot out. She helped the team win by making a two handed stop of a Chinese shot in the last minutes of the game. She competed in the FINA World League Super Finals in Tenerife, Spain, where Australia took home a bronze medal. She won a bronze medal at the 2008 Summer Olympics as a member of the Australia women's national water polo team. Her team ended up in the bronze medal match after losing 8–9 to the United States in the semi finals and playing against Hungary for the bronze. Earlier in the Olympics, her team had tied the Hungarians.
In 2009, McCormack was part of the Australian side that finished third at the FINA World League Super Finals in Kirishi, Russia. She was also part of the team that finished sixth at the FINA World Championships in Rome, Italy, in 2009. In April 2011, she attended a training camp at the Australian Institute of Sport where the coach was "selecting a team for the major championships over winter." She competed in a warm-up match for the 2011 FINA World League against Italy in Ostia, Italy, in July that Australia won 12–11. In February 2012, she was named to the final training squad for the 2012 Summer Olympics. She attended training camp that started on 20 February 2012 at the Australian Institute of Sport. The team of seventeen players will be cut to thirteen before the team departs for the Olympic games, with the announcement being made on 13 June. She was part of the Stingers squad that competed in a five-game test against Great Britain at the AIS in late February 2012. This was the team's first matches against Great Britain's national team in six years.
At the 2012 Summer Olympics, she was part of the team that won bronze.