Ms Davidson, who is expecting her first child with partner Jen Wilson later this year, told how she had suffered terrible mental health problems as a teenager and revealed scars from when she self-harmed.
The 39-year-old’s popularity and electoral success in Scotland, where she revived the party’s fortunes, have seen her frequently tipped as a future leader of the UK party.
Speculation earlier this month suggested she was due to be given a seat in the Lords to put her in the Cabinet and prepare her for leadership.
But Ms Davidson explicitly ruled out a leadership move, also dismissing claims that she could move south and become an MP.
Asked if she would ever run, she said: “No. I value my relationship and my mental health too much for it. I will not be a candidate.”
She added: “On a human level, the idea that I would have a child in Edinburgh and then immediately go down to London four days a week and leave it up here is offensive, actually offensive to me.”
In extracts from Ms Davidson’s memoirs, she tells how the suicide of a boy from her home village when she was 17 sent her into a “tailspin”.
A year later she was diagnosed with clinical depression but the medication gave her “desperate, dark, terrible dreams”.
“I started having suicidal thoughts,” she wrote.
The Scottish Tory leader said she is “still frightened” of going back to the “psychological place I once inhabited”.
She said she turns to “structure, exercise, forward momentum, measurable outcomes” when she is feeling anxious.
The interview was widely praised by politicians from all parties and health professionals for raising the mental health problems faced by teenagers.
David Smith, chief executive of Mind, said: “Put party politics to one side, this is a remarkable story of a mainstream UK political leader talking so openly about their mental health, self-harm and depression.”
John Crichton, chairman of the Royal College of Psychiatrists in Scotland, said: “Thank you Ruth Davidson for speaking out so honestly. We must get our mental health services right for those in school, university and the workplace.”
Scottish Labour leader Richard Leonard said: “Ruth Davidson’s decision to discuss her own experiences including self-harm will mean a great deal to a great many people.
“We must continue to do all we can to end the stigma surrounding mental health.”