Kristina Šmigun was born into a sporting family, her parents both world class cross-country skiers and her younger sister Katrin would also became a cross-country skier. Coached by her parents her entire career, which lasted from 1991-2010, Šmigun became one of the most successful female Estonian athletes ever along with track cyclist Erika Salumäe. During her career, Šmigun won three Olympic medals – golds in 10 km classical and pursuit at the 2006 Olympics and silver in 10 km freestyle at the 2010 Olympics. At the World Championships, she won six medals – gold in pursuit in 2003, silvers in 15 km freestyle in 1999 and in 10 km classical and 15 km classical in 2003 and bronzes in 30 km classical in 1999 and 30 km freestyle in 2003.
Šmigun also won 16 World Cup events during her career and her best place in overall World Cup standings was second in the 1999-00 and 2002-03 seasons. Domestically, Šmigun won 42 Estonian titles between 1991-10 and was elected as Estonian Sportswoman of the Year eight times (1997, 1999-2000, 2002-04, 2006, 2010). Šmigun finished her sporting career after the 2010 Winter Olympics and since 2012 has been vice-president of the Estonian National Olympic Committee. In 2011 she began working as a marketing director of Estonian fast food franchise Näps.