Stafford was born in London, Ontario and grew up in Toronto.[3] Her father James Stafford was a former competitive runner and represented Canada at four World Cross Country Championships. She and her older sister Gabriela DeBues-Stafford initially trained in competitiveIrish dancing, but DeBues-Stafford switched to running, subsequently joined by Stafford to spend more time with her father and sister. Both sisters were diagnosed with Graves' disease as teenagers, with Stafford's case proving a considerable hindrance in her early career.[3]
The onset of the COVID-19 pandemic resulted in the cancellation of much of the 2020 athletic season and the 2020 Summer Olympics in Tokyo being delayed by a full year. For Stafford, this afforded her time to recover from a thyroid procedure that she credited with allowing her to train more consistently.[4] In July 2021, Stafford was named to Canada's 2020 Olympic team in the women's 1500 m event, alongside her sister.[5][6] She qualified to the semi-final, but finished thirteenth overall there, 0.43 seconds behind Spain's Marta Pérez, and missed advancing to the final. Her time of 4:02.12 was a new personal best.[7]
In advance of the 2022 season, Stafford moved to train at the Bowerman Track Club in Portland, joining her sister Gabriela.[8] However, they would both depart the club early in the following year, citing controversy around another club member, Shelby Houlihan.[9] Stafford made her World Indoor debut at the 2022 edition in Belgrade, finishing eighth in the 1500 m.[10] She went on to make her World Athletics Championships debut as well, but came thirty-fourth in the heats of the 4:09.67 and did not advance to the semi-finals. She was also named to Canada's team for the 2022 Commonwealth Games in Birmingham, but her preparations were hindered by contracting COVID-19. Despite this, she qualified to the 1500 m final and finished eleventh, albeit well off her personal best. Stafford reflected that "all you can ask for yourself is to do your best. I know it's very far from where I want to be, but I always count on myself to do my best."[11]
Following her departure from the Bowerman Club, Stafford resumed training in Toronto with longtime coach Terry Radchenko.[12] On January 28, 2023, Stafford broke the North American indoor record in the 1000 metres with a time of 2:33.75 at the Boston University John Thomas Terrier Classic in Boston.[2] She moved to ninth on the world indoor all-time list.[13] After narrowly missing the World Athletics Championship qualifying standard for the 1500 m at the 2023 Millrose Games, she cleared it with a personal best 4:02.03 at the USATF LA Grand Prix on May 27.[14] Stafford finished 28th in the heats of the 1500 m at the 2023 World Athletics Championships, running a 4:05.21.[15] She later described the heat as "probably the most physical race I've been in. When you're competing with the best in the world, there's no room for imperfection."[16]
Stafford is the daughter of Jamie Stafford, a statistics professor at the University of Toronto, and Maria Luisa Gardner, a teacher. When Stafford was 10, her mother died from leukdmia. Stafford has an older sister Gabriela Debues-Stafford, who is also an Olympian runner. She also has a younger brother, Nicholas. Stafford’s family includes her stepmother, Leanne Shafir, and stepsisters, Talia and Gabrielle. [18] Her mother passed away due to leukemia when Lucia was 10.[3] Both Gabriela and Lucia are trilingual, speaking English, French and Spanish.[19]
In the fall of 2022, Stafford enrolled in the singer/songwriter program at Seneca College.[12]
