Born in the parish of
Westmoreland, Jamaica, her mother, Merfelin Spencer was a 400 m runner in college and her father Joshua Spencer was a
middle-distance runner and she followed in their footsteps into the sport of
athletics. She attended the
University of Technology in Jamaica and began focusing on her running under the tutelage of Stephen Francis as part of his Maximising Velocity and Power Track Club. She had her first
hurdles success at the
2006 World Junior Championships in Athletics, where she won the junior 400 m hurdles title with a personal best run of 55.11 seconds. Her debut at the senior level came the following year and she reached the semi-finals of her event at the
2007 World Championships in Athletics in
Osaka. Spencer made a strong start to the 2008 outdoor season by running a world-leading time in the
400 metres at the Azuza Pacific Invitational, winning in a personal best time of 50.55 seconds. She began competing in the
IAAF Golden League in 2009, performing at the
Reebok Grand Prix,
Golden Gala and
Herculis meetings, although she failed to reach the podium on those occasions. At the
2009 World Championships, Spencer reached the final of the women's 400 m hurdles and finished fourth with a personal best run of 53.56 seconds – her club teammate
Melaine Walker won the gold in a championship record. She was also the substitute runner in the
4 × 400 m relay at the championships and helped her team progress to the final where they won the silver medal. She took a victory over Walker shortly afterwards at the
IAAF Zagreb Grand Prix. Spencer ended her season by winning the silver medal at the
2009 IAAF World Athletics Final, running 53.99 seconds to finish behind Walker. and was third in the 400 m at the Jamaican Championships that month. She began making an impact on the Diamond League, finishing as runner-up behind
Lashinda Demus at the
Prefontaine Classic and the Golden Gala, recording a personal best 53.48 s. She had her first win on the major circuit at the
British Grand Prix. She won at the
Herculis meeting soon after and also set a meet record of 53.72 s at the
Spitzenleichtathletik competition in Switzerland. The 24-year-old set a personal best in the 400 m hurdles of 52.79 s at the Aviva Grand Prix in Crystal Palace on 5 August 2011. As a result, Spencer was heavy favourite to win the gold medal at
2011 World Championships in Athletics in
Daegu,
South Korea, where she finished fourth. At the
2012 London Olympics, Spencer initially narrowly missed out on a medal, finishing in fourth place in the 400 m hurdles. She was upgraded to the bronze medal in December 2022, following the stripping of gold medallist
Natalya Antyukh of Russia. Spencer won the gold medal in her specialist event at the
2014 Commonwealth Games held in
Glasgow. ==Achievements==