For 46 years Roger Ebert, who has died aged 70 after suffering from cancer, wrote on films for the Chicago Sun-Times, and did not want to stop. The one thing he welcomed when announcing a "leave of presence" earlier this week was the realisation of a fantasy: "reviewing only the movies I want to review".

His following in the English-speaking world was unrivalled. He and Gene Siskel, his co-host on At the Movies on television, had a street named after them – Siskel and Ebert Way – near the CBS Studios in Chicago where they worked together. In 1975, Ebert became the first film critic to win a Pulitzer prize for criticism.

He has a star on the Hollywood Walk of Fame, and received honorary degrees from various institutions of learning. In 2007, Forbes magazine named Ebert "the most powerful pundit in America".

Why all the accolades? As a race, film critics rarely arouse affection. However, the rotund and bespectacled Ebert had a way of ingratiating himself with his readers even when they disagreed with his lucid and fair reviews. He had a popular touch without ever dumbing down. He would approach every film, whether a masterpiece of world cinema or the latest Hollywood abomination, with the same acuity.

Ebert, who described his critical approach to films as "relative, not absolute", reviewed a film for what he felt would be its prospective audience. But he was aware that "most people choose movies that provide exactly what they expect, and tell them things they already know ... What happens between the time we are eight and the time we are 20 that robs us of our childhood curiosity? What turns movie-lovers into consumers? What does it say about you if you only want to see what everybody else is seeing?"

There were more intellectual and important American critics – he was no Manny Farber or Andrew Sarris – but few were more passionate and personal. He seemed oblivious to the traumatic changes in scholarly film criticism that took place since he started writing reviews for the Sun-Times in 1967. His choice of top 10 movies (for the 2002 Sight and Sound poll) was conventional: Aguirre, Wrath of God; Apocalypse Now; Citizen Kane; Dekalog; La Dolce Vita; The General; Raging Bull; 2001: A Space Odyssey; Tokyo Story; and Vertigo.

Ten years later, for the 2012 poll, he had not altered his opinion one jot, except for, rather startlingly, replacing Dekalog with Terrence Malick's The Tree of Life. Nevertheless, during the first decade of the new century, at a time when film criticism was in crisis – due to the flood of cybercritics drowning out the voices of most professionals – Ebert's views were still heard and listened to even when he was forced to leave TV after losing the ability to speak following an operation, one of many, for thyroid cancer. As the Guardian critic Peter Bradshaw, an admirer, pointed out: "Ebert can blog as extensively as he likes, and he tweets as to the manner born! Even his voice has been recreated for a voice-machine (by a Scottish company), using his extensive archive of DVD commentaries."

Ebert was born in Illinois, a third-generation American, his paternal grandparents being German Catholic immigrants. After graduating from the University of Illinois, Ebert got a job as reporter on the Sun-Times, where he stayed for the rest of his career. In 1970, he co-wrote the screenplay for the Russ Meyer film Beyond the Valley of the Dolls. It was a rare excursion into big-budget cinema by Meyer, who had gained a cult following in the 1960s with his "nudie-cutie" films. It turned out to be Meyer's favourite: "Roger and I embraced that one to our bosoms, or co-bosoms," he explained. The film is a self-styled morality tale in which each character represents a vice or a virtue. The diaphanous plot, with a lot of perverted sex, drugs and backstabbing, concerns an all-girl rock group, the Carry Nations, handled by Z-man Barzell (John Lazar), who has lines like "You will drink the black sperm of my vengeance." Ebert's fellow critic Alexander Walker described it as "a film whose total idiotic, monstrous badness raises it to the pitch of near-irresistible entertainment". Ten years after its release, Ebert had the chutzpah to write a rave review of it. He wrote two further films with Meyer, Up! (1976), this time hidden under the name of Reinhold Timme, and Beneath the Valley of the Ultravixens (1979), both featuring violence and Meyer's trademark huge breasts. The wonder was that Ebert was ever taken seriously as a film critic again. Actually, the fact that he had written screenplays, whatever their value, perhaps gave him more credibility.

Although he was seldom cruel and gave the impression of always wanting to like a film, he never pulled his punches when he felt that the target deserved it. For example, reviewing Rob Reiner's North (1994), he expostulated: "I hated this movie. Hated hated hated hated hated this movie. Hated it. Hated every simpering stupid vacant audience-insulting moment of it. Hated the sensibility that thought anyone would like it. Hated the implied insult to the audience by its belief that anyone would be entertained by it." Ebert was in the majority in his excoriation of Michael Cimino's Heaven's Gate (1980). "I know, I know: he's trying to demystify the west, and all those other things hotshot directors try to do when they don't really want to make a western. But this movie is a study in wretched excess. It is so smoky, so dusty, so foggy, so unfocused and so brownish yellow that you want to try Windex on the screen. A director is in deep trouble when we do not even enjoy the primary act of looking at his picture ... his movie is $36m thrown to the winds. It is the most scandalous cinematic waste I have ever seen, and remember, I've seen Paint Your Wagon." Ebert's reactions were primarily instinctive rather than cerebral, as evident in his review of Ingmar Bergman's Cries and Whispers (1972): "It is hypnotic, disturbing, frightening. It envelops us in a red membrane of passion and fear, and, in some way, that I do not fully understand, it employs taboos and ancient superstitions to make its effect. We slip lower in our seats, feeling claustrophobia and sexual disquiet, realising that we have been surrounded by the vision of a film-maker who has complete mastery of his art." In 1975, Ebert and Siskel, of the Chicago Tribune, began co-hosting a weekly film review television show, Sneak Previews, for the Chicago public broadcasting station. The show was picked up by PBS in 1978 for national distribution. A year later, partly at the instigation of Siskel, Ebert, a recovering alcoholic, quit drinking and became a member of Alcoholics Anonymous. In 1982, the duo moved to a syndicated commercial television show named At the Movies, where they became widely known for their "thumbs up/thumbs down" reactions to films. After Siskel died aged 53 in 1999, Ebert teamed up with Richard Roeper for a show that ran until 2006. This was the year that Ebert suffered post-surgical complications and lost his voice. In 2010, Ebert had his lower jaw removed, yet he continued to be as active as possible, helped by the trial attorney Charlie "Chaz" Hammel-Smith, his wife since 1992, who survives him.

• Roger Joseph Ebert, film critic and screenwriter, born 18 June 1942; died 4 April 2013

Ronald Bergan