Her daughter Maggie McGuane said on Wednesday that it was a "big relief" to have the truth out.
Kidder said at the time she was first diagnosed with bipolar disorder eight years earlier, but refused to take the lithium that was prescribed to her.
The actress found fame starring alongside Christopher Reeve in the Superman films of the 1970s and 1980s. She believes it is important to be open and honest about suicide and not hide it.
Now, nearly three months after Kidder's body was found by a friend in her Livingston, Montana home, a coroner there has ruled her death a suicide.
She spoke openly about how she had wandered around Los Angeles for days during that episode, and she said in 2008 that she did not like the words "mental illness".
Kidder, like Carrie Fisher, was an advocate for ending the social shame surrounding mental health issues.
She added, referring to the high suicide rate in Montana, "It's a very unique sort of grief and pain". A friend discovered Kidder's body at her home on May 13th. Kidder also appeared on the Smallville TV series, and she most recently appeared on The Neighborhood as Maggie. "Knowing how many families in this state go through this, I wish that I could reach out to each one of them".
She also appeared in 1978's The Amityville Horror.
If you or someone you know is dealing with suicidal thoughts, you can call the National Suicide Prevention Lifeline at: 1-800-273-8255.