The 27-year-old actress addressed her estranged relationship with the 66-year-old singer in an open letter in Unfiltered: No Shame, No Regrets, Just Me.
"We all make choices and, although I don't excuse some of yours, at the end of the day we can't rewrite the past," Lily Collins wrote. "I'm learning how to accept your actions and vocalize how they made me feel. I accept and honor the sadness and anger I felt toward the things you did or didn't do, did or didn't give me.
"I forgive you for not always being there when I needed and for not being the dad I expected," she added. "I forgive the mistakes you made. And although it may seem like it's too late, it's not. There's still so much time to move forward."
Lily Collins is the daughter of Phil Collins and his second wife, Jill Tavelman, who divorced in 1996. The singer subsequently moved from Britain to Switzerland, which Lily Collins said had a harmful effect on her.
"Because my dad was often gone, I never wanted to do anything that would make him stay away even longer," she shared. "I became extra careful about what I said and how I said it, afraid he'd think I was angry or didn't love him. And the truth is, I was angry. I missed him and wanted him there.
"I've realized that many of my deepest insecurities stem from these issues with my dad," the star said. "It's taken me over a decade to resolve some of them (others I'm still resolving) and to finally build up the courage to speak my mind to him."
The Okja actress also said her dad's divorce from third wife Orianne Cevey fueled her onetime eating disorder. She had discussed her struggle with anorexia in an interview with IMDb Studio in January while promoting her movie To the Bone.
"This was definitely a more dramatic role for me. I suffered with eating disorders when I was a teenager as well," the star said. "It did require a different set of emotional skills, to kind of go back in time for me."