The actress said it started when she was around 8 years old, which was the same time her mother Pandora was struggling with addiction to heroin. Her depression worsened as a teen.
"I think I properly started dealing with depression when I was about 16, when all the stuff with my family started to make sense and came to the surface," she told Esquire magazine.
"I'm very good at repressing emotion and seeming fine. As a kid I felt like I had to be good and I had to be strong because my mum wasn't," she continued. "So, when it got to being a teenager and all the hormones and the pressure and wanting to do well at school -- for my parents, not for me -- I had a mental breakdown."
"I was suicidal," Delevingne, 23, admitted. "I couldn't deal with it any more. I realized how lucky and privileged I was, but all I wanted to do was die. I felt so guilty because of that and hated myself because of that, and then it's a cycle. I didn't want to exist anymore. I wanted for each molecule of my body to disintegrate. I wanted to die."
Despite her troubled childhood, the actress described her mother as "incredible."
"She always had so much love," she added. "And I felt like when I was a kid I was kind of like her confidante. I really felt like I understood her and how she was feeling and why."
"Modelling is not something I love," she said. "It always felt like a job. It was never a passion. It was more like a part I played."
"There are some girls who are beautiful all the time, that's just who they are. I'm not," she explained. "I'm a weirdo, I'm a goofball. I just don't ever feel like I look that pretty. And so when I do all the posing, that just feels so stupid to me."
For now she's focusing on her acting career -- which has her hitting the big screen in "Suicide Squad," out today -- non-stop.
"If I stop, I go crazy. I lose my mind. I just kind of break down a little bit," she said.