At the 2005 World Championships in Athletics, she won a silver medal. At the 2006 Commonwealth Games in Melbourne, Australia, she received a bronze medal for her third-place finish in the 400 metres. At the 2012 Olympic games, Williams-Mills won a silver medal in the 4×400 meter relay. She also placed 5th in the individual 400 m event. Williams-Mills missed most of the 2013 season due to undergoing treatment for breast cancer. During the 2014 season, Williams-Mills was very successful. Early in the season, she and three other Jamaican women won a silver medal in the 4 × 400 m relay at the 2014 world relays. Williams-Mills competed at the 2014 Commonwealth Games in Glasgow and won a silver medal in the individual 400 m and a gold in the 4 × 400 m relay, setting a games record in the latter. She was also successful at Diamond League meets, where she was crowned the 2014 Diamond League champion in the 400 m. In 2015, Williams-Mills again won a silver medal at the world relays as part of the Jamaican 4 × 400 m team. At the 2015 World Championships in Athletics in Beijing, Williams-Mills finished sixth in the 400 m final involving four Jamaican women. In the relay, along with Christine Day, Shericka Jackson and Stephenie Ann McPherson, the individual 4th, 3rd and 5th placers, respectively, the Jamaican team won gold in front of the American favorites by just outsprinting them in the last 50 metres. In 2016, Williams-Mills only competed in the relay at the 2016 Olympic games, running as the anchor leg for Jamaica trying to pass Allyson Felix of the US, but during the final stretch Allyson manage to hold off Novelene to get gold for the US and Jamaica got silver. In 2017, Williams-Mills won the 400 m at the Jamaica invitational, winning in a time of 50.56. Later on in the season, she also won the 400 m at the Diamond League meeting in Paris in a time of 51.03. At the London 2017World Championships, Williams-Mills made the final of the women's 400 m and came in eighth place in a time of 51.49. In the 4 × 400 m relay, which was going to be her last major championship race, she was scheduled to anchor the Jamaican team; however, on the second leg, Anneisha McLaughlin-Wilby pulled up injured, therefore ending the Jamaican team's chances of medalling in that event. During the 2017 season, Williams-Mills announced that she would retire at the end of the 2017 season “ This is my farewell season; I’ve been in this for a long time and I think I’ve done my fair share and represented my country well so sometimes you have to hang up your spikes and move on the next chapter of your life and I think I’ve reached that point where I need to do that now,” said Williams-Mills. Her last race was on September 1st 2017 at the Brussels Diamond League, where she came 6th place running 51.27.
Cancer diagnosis
In July 2013, Williams-Mills told members of the media that she was diagnosed with breast cancer before the 2012 Olympics. Very few people at the time knew about the diagnosis. Despite the diagnosis, she still ran the race and was able to help Jamaica win a bronze medal. After the Olympics, Williams-Mills had a mastectomy and in January 2013, had another operation. She has stated that she would run, "for all the breast cancer survivors out there."
