Speaking on US TV show The Talk, the gospel artist revealed how she struggled to deal with depression and mental health issues as a teenager before joining the Beyonce Knowles-Carter headed group aged 20.
The 'Say Yes' singer explained: "For years, I'm in one of the top-selling female groups of all time suffering with depression."
However, it wasn't until her thirties that she was able to understand what she was going through.
During her time in the girl group, Beyonce's father Mathew Knowles - who was the group's manager - also struggled to understand why she felt the way she did.
She said: "It got really really bad to the point of I was suicidal.
"I was to that place where it got so dark and heavy because sometimes you feel like 'I'm the provider, I take care of people, I'm not supposed to be feeling this way - what do I do?' I wanted out."
Williams was a member of the group between 2000 and 2005, alongside Beyonce and Kelly Rowland.
She told the CBS talk show that she had been inspired to speak out about depression by fellow musician Demi Lovato, who has been vocal about her own mental health problems.
This follows a growing number of artists who have also decided to speak out about mental health.
Christian grime artist Stormzy previously struggled with depression, and shared these experiences in tracks on his debut album 'Gang Signs & Prayer'.
