Lucy Charles-Barclay (born 15 September 1993) is an English professional triathlete specialising in the Ironman and 70.3 ("half-Ironman") distances.

Prior to taking up triathlon, Charles was an elite distance and open water swimmer.

She attempted to gain selection for the British swimming team for the 2012 Olympic trials in both the pool and open water.

She was, however, unsuccessful, despite having beaten open water trials winner Keri-anne Payne in the Great North Swim a month previously.

Charles subsequently made her debut in triathlon in 2014 and went on to win the 18–24 women’s age category at the 2015 Ironman World Championship as an amateur.

Charles who was still a teenager at the time was so devastated, that at some point in 2013 she lost the motivation to only keep swimming for the next Olympic opportunity in 2016.

At the 2018 Ironman World Championship in October she again landed in second place behind Daniela Ryf and broke the swim record with 48:13 minutes.

[5][9][10] In 2019, Charles won Challenge Roth and the European Ironman Championships with her personal record of 8:31:09 hours for the entire race.

In 2024, she received two second place finishes at the PTO T100 World Tour, one to India Lee in Miami and another one to Ashleigh Gentle in Singapore.

She announced that she planned to validate her slot for the 2024 Ironman World Championships held in Nice, France.