Arthur Miller’s anger at the death of his second wife Marilyn Monroe is expressed in an excoriating and never before published essay from 1962, in which the playwright attacks the “public mourners” who “stand there weeping and gawking, glad that it is not you going into the earth, glad that it is this lovely girl who at last you killed”.

The playwright’s essay is one of many unpublished works found in an extensive archive of manuscripts, notebooks and letters that has just been acquired by the Harry Ransom Center at the University of Texas at Austin, for a sum the New York Times put at $2.7m (£2m).

Drafts of Miller’s plays All My Sons, Death of a Salesman, The Crucible and A View From the Bridge are in the archive, which the Times said stretched to “322 linear feet of material”. There are also more than 50 of the journals in which the playwright recorded ideas, drafts, bits of dialogue and reflections on his life, from the 1940s to the 2000s.

“It’s rare to see a writer document his process in such a rich and complete way,” said Eric Colleary, the Ransom Center’s Cline curator of theatre and performing arts. “Given the scope and scale of Miller’s archive, researchers and artists can look forward to significant new insights into one of America’s greatest playwrights and public intellectuals.”

Many unpublished works feature in the archive, including the 1962 essay about the death of Monroe – to whom he was married from 1956-61 – which Miller revised over a number of years but never published. “Instead of jetting to the funeral to get my picture taken I decided to stay home and let the public mourners finish the mockery,” he wrote. “Not that everyone there will be false, but enough. Most of them there destroyed her, ladies and gentlemen.”

Part of the archive relates to the investigation into Miller by the House Un-American Activities Committee. Miller’s play about the Salem witch trials, The Crucible, drew heavy parallels with the communist witch-hunts of the time. Miller refused to support the decision by director Elia Kazan to provide the names of suspected communists to the committee, and in a 1952 letter to Kazan’s wife Molly, who had attacked him for this decision and for drawing parallels between witches and communists in The Crucible, he defended his approach. “This committee’s mentality, and the atmosphere which it has engendered after almost 15 years of ceaseless propaganda, are such as to throw perfectly honest people into a kind of nameless fear which is utterly destructive of a sane order of life,” wrote Miller.

In another response to criticism of The Crucible – this time from the American Bar Association, for being “disparaging of lawyers” – Miller also showed his lifelong commitment to defending free speech. “The growing sensitivity of people to any sort of open and frank discussion of important issues is no service to civilisation, let alone law and order. I wrote a play about a man who happened to be a salesman, and several organisations of sales people flew to arms. Now it is the lawyers. If I am to back away from these objections you must surely see that I shall be forced to write about people with no occupation whatever,” he responded in 1953. “But then café society will probably feel put-upon … In defense of my right to speak, therefore, and to write the truth as I see it, I must insist upon the play as it stands.”

The Ransom Center, which is already home to archives of playwrights including Tennessee Williams, Samuel Beckett and David Mamet, said that Miller first donated early play manuscripts and notebooks to its collection in the early 1960s, and that the new acquisition “greatly extends” its archive. “Arthur Miller is one of our country’s finest playwrights, one who gave dramatic form to themes that are central to our still-evolving American story,” said Ransom Center director Stephen Enniss. “For years to come, all primary source research into this major American playwright’s life and work will begin here.”

Miller’s son Robert A Miller said that the family was “pleased to have found a fitting home for Dad’s voluminous notes”.

The new materials will be catalogued within two years, and the collection will then be available to researchers and the public.