The All My Sons playwright was married to the Hollywood actress for five years and their divorce was finalised just over 18 months before the Some Like It Hot star died aged 36 after suffering a barbiturates overdose in 1962.
Now newly unearthed recordings have revealed Miller - who died in 2005 - always feared Monroe would meet a tragic end.
In taped conversations with his friend and biographer Professor Christopher Bigsby - published by the Guardian newspaper - Miller said of his ex-wife: "One time I brought doctors to pump her out because she had swallowed enough stuff (drugs) to kill her.
"So I felt she was in a very delicate psychological position. As it turned out, it took some years, but it happened. It was beyond my powers or anybody else's to hold her back ...
"It was impossible for her to live, let alone with anybody. You couldn't go on with that intensity of life, and those drugs, and manage to survive."
In the tapes, Miller also discusses their pair's volatile relationship - admitting he was "not really prepared" for what life with Monroe was going to be like, explaining: "I was not really prepared for what I should have been prepared for, which was that she had literally no inner resources …
"She wanted a father, a lover, friend, agent, above all someone who would never criticise her for anything, or else she would lose confidence in herself. I don't know if that human being exists."
Miller also talked about Monroe's longing to become a mother, confessing he thought having a baby would have become an "additional problem" for her.
He said: "In a way, I am not sure how good it would have been for her to have a child. It would have been an additional problem … I am not sure how it would have worked out in practice."
However, Miller was also full of praise for his former partner describing her as a "very smart woman" and pointing out her "terrific" sense of humour and generous spirit.
The esteemed playwright revealed Monroe began spiralling in later years and was overcome with a sense of paranoia which caused her to suspect everyone around her was "exploiting or damaging her".
Miller explained the difficult end of the marriage revealing they weren't speaking at all by the time Monroe obtained a divorce in January 1961 but he revealed he would have ended the union anyway if the actress hadn't done it herself.
"She was genuinely hostile to me ... I couldn't have gone on. It would have killed me. I couldn't work anymore," he said.
9°C