John Lahr has something to show me. Up the stairs we go, to the fourth floor of his tall and forbiddingly elegant house in north London. He prods open a door. “The writing room,” he declares. In the gloom is an Aladdin’s cave. Above the avalanche of papers on the desk, there is a portrait of Ingrid Bergman by the artist Paul Davis. Across the room is a clapperboard from the set of Prick Up Your Ears, the movie version of Lahr’s biography of Joe Orton. Above is a black and white photograph of Lahr himself, by his friend Richard Avedon. I spy a handwritten letter on the mantel. “Thank you for the piece,” it reads, in loping handwriting. “The best thing about my stuff I have ever read.” I look closer: Arthur Miller’s notepaper.

To say that Lahr lives and breathes showbusiness is an understatement. The son of comedian Bert Lahr (famous for his role as the cowardly lion in The Wizard of Oz) and a former Miss Cincinnati, Lahr occupied until recently American theatre’s equivalent of an archbishop’s chair: senior drama critic for the New Yorker. He has written an intimidating number of books, among them superlative studies of Orton and Tennessee Williams. In an industry not known for its love of reviewers, he remains the only critic in history to have won a Tony award (2002, for a show with Broadway powerhouse Elaine Stritch). Back downstairs, fussing with the coffee machine, he starts on a childhood memory of hanging out with Groucho Marx. His blood must be at least three-fifths greasepaint.

“People piss on theatre critics from a great height,” he says, with a dry laugh. “But in the end, they are the record. You can’t replay this stuff. They are the only way we can find a way back.”

Lahr is in retrospective mood, about to publish a collection of reviews and interviews distilled from half a century of avid, addicted theatregoing. Entitled Joy Ride, it is, above all, a tribute to those Lahr affectionately calls “show people” – the “athletes of their spirit” who slog their guts out night after night for us, the shirkers and schmucks in the audience.

Crafted in Lahr’s polished prose, it is studded with anecdotes: meeting, as a starstruck 26-year-old, Harold Pinter in a diner on 45th Street in New York; being given a hunting knife by David Mamet. If you’re curious about Ingmar Bergman’s obsession with punctuality, or what it feels like to go through a Broadway opening in the carpet-chewing company of Tony Kushner, the book is – like Lahr himself – engaging and loquacious company.

One of his earliest memories is of playing in the dust of his father’s Broadway dressing room, but Lahr says Bert never wanted his offspring to stray too close to the limelight. Though John and his sister, Jane, were offered movie contracts (“We were pretty children”), they were instructed to get an education. When Lahr was at Yale, he was attracted to news journalism. Dispatched to the University of Mississippi to cover civil-rights protests there in 1962, he charmed his way in and escaped with a run of front-page stories. Even this ambition, he concedes, was somewhat showbiz-inflected. “I was thinking foreign correspondent, phone booth, cigarettes – the whole look.”

When he came to write something more substantial, what emerged was a biography of his father. Entitled Notes on a Cowardly Lion, it was published in 1969 and contains, one feels, the grains of everything Lahr has subsequently tried to do. “My father had been written about, but had not been seen. He had enough good reviews in his lifetime to fill this room, but only one or two made any sense. I want to leave a record of theatricals that honours the enterprise.”

The book’s success led Lahr into an enviable, if dubious, double life: a reviewer who was employed by the Village Voice, and simultaneously the literary manager of New York’s Lincoln Center, responsible for selecting plays. Though he hasn’t worked directly on a theatre production since the Stritch show in 2001 (it ended in legal action over royalties), the duality lived on at the New Yorker, where he perfected the art of the review-interview, a longform piece that combines behind-curtains encounters with an artist as well as criticism of the work. When I ask him who he has in mind when he writes, he doesn’t blink: “The artists. I’m not there to be a shopping guide for the audience.”

It’s a complicated trick to pull off, I suggest, being both gamekeeper and poacher, prosecutor and defendant. He looks pugnacious. “Many good critics have been in the theatre. They slept on both sides of the bed. You can’t have that knowledge without submerging yourself on both sides.”

Has it ever lost him friendships? “Well, I’ve had death threats, because I didn’t like a Sondheim musical.” Not from Sondheim himself? “Anonymous. But seriously, if you’ve been really engaged and the artist realises that, and you still don’t like the work, well, they don’t love it – but they don’t feel offended.” He muses a moment. “Woody Allen asked me to go to a basketball game when I was writing a profile of him. Much as I wanted to, I couldn’t do it.”

There is another deeply unusual facet of Lahr’s career: for the entirety of his New Yorker stint, he lived 3,500 miles away. In 1974, he moved to London with his first wife, Anthea Mander. (He is now married to actor Connie Booth, best known as Polly in Fawlty Towers. When Tina Brown offered Lahr the New Yorker job in 1992, it was agreed he could commute. For 21 years, he kept to a rigorous schedule: fly to New York on Thursday, catch a show that night, another on Friday, another on Saturday. Sunday was reserved for writing, Monday for editing, after which the reviewing would recommence on Thursday. He’d fly back to London the following Tuesday, only to repeat the whole cycle two weeks later.

How on Earth did he manage it? Another dry chuckle. “It’s easy if they fly you first class. After the banks crashed in 2008, that all changed. Economy for Johnny.” I wonder if it changed his view of theatre, seeing it on both sides of the Atlantic, almost simultaneously. “It certainly gave me a different experience of American life. The English don’t realise they are a culture of scarcity. America is a culture of abundance, even now.” So he isn’t pessimistic about the state of Broadway? He shrugs. “It’s a commercial bubble that never changes. It’s the same, only worse. There’s no sense in slagging it off.”

One thing Lahr is less than buoyant about is the state of criticism. In 2013, he published a piece lamenting that it was a dying art, and arguing for a distinction between critics and what old theatre hands sniffily call “crickets” – writers who chirrup away, contributing nothing of value. “I’m very pessimistic,” he reflects. “The nature of journalism has changed. I would say that there are now only four or five papers in the US where a critic could make a living.” Hasn’t criticism shifted, though, to online magazines, collaborative blogs and the like? “If you want an opinion, you can get it on the web. But who’s giving that opinion?” He injects the o-word with considerable scorn. “I’m not interested in opinion.”

Although he has continued to write for the New Yorker, he hung up his reviewer’s notebook in 2013. He still goes to the theatre, but looks deflated when I mention it. “When I was reviewing, it felt like I was preparing to play a game. Now when I go as a civilian, that urgency isn’t there. I miss the urgency.” He has no ambitions to review anywhere else, he adds. “When the New Yorker ended, that was it. I wanted to retire a Yankee.”

He’s writing as much as ever for the magazine, though, notably a series on trout fishing, which he loves as much as theatre (more, some days). If the estate will agree, he’s pondering a biography of film-maker Mike Nichols, who died last year – another friend. “The idea of me not writing isn’t a happy one,” he says.

I’m struck, I say, by the title of his book. The word “joy” sometimes seems unfashionable in theatre, which has a habit of taking itself too seriously. “Oh, but joy is difficult,” he responds. “To drive people crazy with pleasure? That’s hard to do.”

• John Lahr’s Joy Ride is published on 10 September. To order it for £24 (RRP £30), go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99. Lahr will appear with Michael Billington and Josie Rourke in a Guardian Live event in London on 30 October.

• This article was updated on Friday 4 September, to reflect that no lawsuit resulted from the royalties dispute with Elaine Stritch – it was settled out of court.