Williams was born in Maryland on November 20, 1995 to parents, Tony and Marlene Williams. As her parents are both from Jamaica, Williams is eligible to compete for that country in FIG international competitions. Through her mother, Williams is a niece of Jamaican politician Anthony Hylton.
She grew up in Randallstown, Maryland and graduated from Roland Park Country School in 2014. She is currently attending University of California, Berkeley and is a member of the Golden Bears gymnastics team.
She has three sisters, Maya, Kristine and Zitafa. Her sister, Maya, is also a gymnast on the Jamaican National team.
Toni-Ann trained at United Gymnastix in Reisterstown, Maryland throughout her whole club career. She moved up to Level 10 in 2009 and joined the Jamaican national gymnastics team in 2010.
In 2011, she was State and Regional Champion and competed in her first international competition, the 2011 World Artistic Gymnastics Championships in Tokyo, Japan.
She was hoping to qualify to the 2012 Olympics but was unable because she didn't meet requirements at the 2011 Worlds. In 2012, she was again crowned State Champion.
Williams represented Jamaica at her second World Championships in 2013, in Antwerp, Belgium.
In 2014, Toni-Ann was State Champion for the fourth time in her Level 10 career.
Williams' first season in the NCAA was during the 2015 season for the California Bears.
Williams quickly became one of Cal's top gymnasts to ever compete in the program, even in her freshman season. On February 13, 2015, during a regular season meet against Oregon State, she broke the school record on vault, scoring a 9.975.
During the regular season, she peaked at #1 nationally on floor on February 23, 2015 and has reached as high as #5 nationally on vault (on March 2, 2015). She qualified to the 2015 NCAA Women's Gymnastics Championships as an individual all-arounder.
In February 2015, it was announced that she and British gymnast and UCLA gymnast, Danusia Francis, would participate at the 2015 World Artistic Gymnastics Championships and try to qualify for the 2016 Olympics in Rio de Janeiro.