Flanagan grew up in Marblehead, Massachusetts. She attended Marblehead High School, where she excelled in cross country and track. She also participated in soccer and swimming, and was a talented artist and painter in the art major program. Her Marblehead HS accomplishments included three-time All-State cross country performances, a first-place All-State finish in the mile, and a two-mile win whose record still stands; her 4:46 mile won the Indoor National Scholastic Championships. She attended the University of North Carolina-Chapel Hill, where she won national cross country titles in 2002 and 2003 — becoming the first individual champion in the sport in Tar Heel history — and numerous track accolades, with best times of 4:11.24 in 1500 m (7th in the US at any level in 2003,) 9:00.22 in the 3000 m, and 15:20.54 in the 5000 m.
Since advancing to the professional level in 2004, she has lowered her 3000 meter time to 8:33.25 and her 5000 meter time to 14:44.80, the latter an American record at the time; her 1500m record has slightly improved to 4:05.86. She is a two-time national champion in the women’s 5000 meters.
Flanagan ran the 10000m for the first time at the 2008 Stanford Payton Jordan invite meeting, in a time of 30:34.49 to beat Deena Kastor’s American record of 30:50.32.
At the 2008 Summer Olympic Trials held in Eugene, Oregon Flanagan competed in both the 5000m and 10000m. She won the 10000 m final in a time of 31:34.81. This guaranteed her a spot on Team USA for 2008 Olympic Games. Flanagan also finished third in the 5000 m final with a time of 15:02.81.
On August 16, 2008, Flanagan finished 3rd in the 2008 Olympic Womens 10000m Finals in Beijing, capturing the Bronze medal. She also set a new American record in 30:22.22, shattering her own American record set earlier in the year. She is only the second American woman to receive an Olympic medal in the 10,000 m.
Flanagan has been one of the U.S.’s top cross country runners for more than a decade from her 2000 win of the USA Junior XC Championships through to her 2011 individual bronze medal at the IAAF World XC Championships where she also helped to lead the U.S. women to a team bronze.
Shalane’s mother, Cheryl Treworgy, is a former women’s marathon world record holder and competed at the World Cross Country Championships in 1968 (11th), 1969 (4th), 1970 (18th), 1974 (28th) 1976 (38th).