Peter Tosh was not a man of peace. He was a revolutionary. "Peace," he told the feverish 40,000-strong crowd at the famous One Love Peace Concert in 1978, is "the diploma you get in the cemetery", written on your tombstone: "Rest in Peace!"

Tosh believed in action. Standing 6ft 4in in his black beret and often wielding a guitar shaped in the form of an M16 assault rifle, he was the most militant member of the world's greatest reggae band, The Wailers. Next to him, Bob Marley looked like a mere pop star.

He knew what he was doing that charged evening as he strode to the microphone in his black martial arts uniform and put his life on the line in one of the most passionate and dangerous political speeches ever given by a musician. Addressing Jamaica's two leading politicians, Prime Minister Michael Manley and Edward Seaga, the Leader of the Opposition, as they sat before him at a time when the country was being rent apart by murderous political gun battles in its poorest districts, Tosh warned: "Hungry people are angry people".

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Retribution was inevitable, and came five months later. He was taken into a police station and beaten relentlessly until his skull cracked open and the hand he attempted to shield himself with was broken. He only survived by playing dead.

Today, Tosh is relatively unknown. The One Love Peace Concert went down in history because Bob Marley called Manley and Seaga on stage and made them shake hands in front of the television cameras. Tosh's earlier, braver action was not televised because he ordered the "lickle pirates from America... wid dem camera and dem TV business" to stop filming. In the recorded version of that night, and in the history of popular music, Peter would be overshadowed by Bob, the man who he taught to play the guitar.

And yet, after a long hiatus in which the Jamaican establishment, that was so stung by his criticisms, had almost succeeded in expunging Tosh from an island soundtrack defined by tourist-friendly Marley anthems such as "Jammin'" and "Could You Be Loved", the legacy of Peter Tosh is now being recognised.

He is the subject of a biography, The Life of Peter Tosh: Steppin' Razor, by the British author John Masouri. The Oscar-winning director, Kevin Macdonald, is planning a feature based around the making of Tosh's first great solo album Legalize It. In October, near his family home in the rural Jamaican parish of Westmoreland, a two-day concert – Earth Strong Celebration – took place in the Peter Tosh Memorial Garden.

Last year, the governing People's National Party – which Tosh supported – awarded him Jamaica's great honour, the Order of Merit, which was bestowed on Marley in the weeks before Bob's death from cancer in 1981.

It is 26 years now since Tosh's own passing. He was the victim of a treacherous murder, robbed and slain in his own home by an acquaintance: a brutal example of the desperate ghetto behaviour he had warned Jamaica's leaders about. Whereas Marley's funeral was a global news story and brought Jamaica to a standstill, Tosh's burial was a fiasco. His mother had to disown one of the two 'fathers' who turned up and the service was interrupted by protesters, including one who stood by the coffin and implored the body to "Arise and open the casket!".

It's not clear how Peter Tosh, with all his revolutionary tendencies – musical and otherwise – would have regarded these belated celebrations of his memory and establishment-type attempts to reclaim him.

For Masouri, who compiled his biography over four years and based it on 100 interviews, Tosh's persona was exemplified by his relationship with the Rolling Stones. The band made him the only signing to their record label and hoped to gain credibility from association with an uncompromising iconoclast.

"He was even too hot for the Rolling Stones to handle," says Masouri of the short-lived relationship. "He was so principled and their hedonistic rock'n'roll lifestyle didn't interest him – he was genuinely revolutionary in his thoughts and ambitions for his music and he really did want to change the world with his songs."

Mick Jagger sung with him on a duet and gave him a hit ("Don't Look Back"), and the Stones released his music (the album Wanted Dread & Alive) and took him on their stadium tour, introducing him to new audiences. But it wasn't enough for Tosh. "He accuses them of not promoting him properly!" says Masouri. "I think they were intimidated by him, although they would never admit to that. But he was too much for them and for many other people as well."

As Tosh sang: "I'm like a steppin' razor, don't you watch my size, I'm dangerous!"

One of Tosh's anthems is titled "I'm the Toughest". He was so physically fit that when he performed a karate move he could look like he was doing the splits in mid-air. He was also a linguistic gymnast who developed a fiery language all of his own, switching the structure of words to give them new significance.

Tosh was the 'Herbalist Verbalist', in the phrase of the American reggae writer Roger Steffens. "He would rip the language apart to reveal its true meaning. 'Be careful of your friends,' he would say, 'they will fry you in the end'. And his manager was his 'damager' and a judge was a 'grudge'. As for politicians, he talked of a 'Crime Minister' who 'shits' in the 'House of Represent-a-t'iefs'."

A son of British colonial Jamaica, Tosh was even more disrespectful of the monarch, declaring: "Queen 'Ere Lies a Bitch".

But Tosh was very serious about his politics. He was a strident campaigner against apartheid and refused invitations to perform in South Africa (playing instead in neighbouring Swaziland). As early as 1979 he was refusing to perform in Israel because of his support for a Palestinian homeland.

The same year – because of his espousal of the anti-nuclear cause – he was given another great promotional opportunity when booked to appear alongside Bruce Springsteen at Madison Square Garden as part of a series of giant anti-nuclear protest concerts. Tosh was advertised to appear in the accompanying film and on the triple LP box set.

"Peter was in pole position," says Masouri. "He walked on stage smoking his ganja spliff and wearing Palestinian dress – it was Jewish New Year and he was in New York. He really did have balls – but he never appeared on the film or on the album."

Nonetheless, in 1987, months before his murder, he made his own album, No Nuclear War. Posthumously, it won him a Grammy.

"A lot of the stuff he sung about, he believed it," says Michael Barnett, a lecturer at the University of the West Indies who has organised a number of symposiums on the anniversary of Tosh's birthday to recognise the significance of his career. "It was not just a superficial thing for him. He put his life on the line for all those concepts and ideas."

The great Jamaican music producer Bunny Lee knew Tosh well during his career and says the artist's themes have contemporary relevance. "Young people should think of Peter Tosh as a great revolutionary in music – and as a person. He believed in truth and rights. His words were, 'Everyone is crying out for peace, no one is crying out for justice' ... He was not afraid to speak his mind right up until it cost him his life."

Initially backed by his band Word, Sound and Power, which featured drummer Sly Dunbar and bass player Robbie Shakespeare (who together comprise reggae's finest rhythm section), Tosh made seven solo albums, including the pro-marijuana Legalize It (made for Richard Branson's Virgin label) and the militant Equal Rights, featuring the anthem "Get Up, Stand Up", which he had created with Marley before the split of The Wailers.

The 1974 breakaway by Bob from Peter and Bunny Wailer – who began working together as a vocal harmony group in 1963 – was a source of acrimony for the remaining two (who had refused to go on tour). "You have the situation where Bob Marley calls his backing band The Wailers," says Masouri. "It was an outrageous thing to do – as if Mick Jagger had formed a new band, Mick Jagger and the Rolling Stones. Peter and Bunny both blamed Bob because he agreed to it. To them, Bob betrayed them."

After Marley died in 1981, Tosh appeared to resent the shadow his great friend cast over the future of Jamaican music. He even rejected the idea that, after Marley's death, he was the "new King of Reggae", telling Steffens that there was "nothing new" about him. During the remaining six years of his life, he would never really sit on that throne.

Masouri says that in Tosh's latter years many white music journalists seemed intent on baiting him – even suggesting he was not black enough because this former harmony singer dared to record the occasional ballad. He was mocked for his observations – often attributed to his copious use of marijuana – and the British music paper Melody Maker even dubbed him 'Fruitcake of the Year'.

"Maybe they were scared of his uncompromising blackness," says Masouri. "Because of his prodigious ganja use I think they dismissed his opinions – especially anything to do with Rastafari. It was almost like they used that as an excuse not to have deal with what he was talking about."

Black Americans could also find Tosh difficult, given his Rastafarian sympathies for repatriation to Africa. "He hated disco music – for him music was not for partying," says Masouri. According to Steffens, Tosh would hector African-Americans for only being interested "in middle-class luxury".

But away from the cameras and microphones, the 'Steppin' Razor' was a less abrasive figure. Lee Jaffe, who shot the striking cover image for Legalize It, featuring Peter smoking his chalice pipe in a secret marijuana plantation in the Jamaican countryside, remembers Tosh as being great company away from the media gaze.

"He was funny and ironic and always twisting up words that made a lot of sense. He was fun to be around," says Jaffe, whose friendship with Tosh is the subject of the Macdonald film. "People talk about his militancy but he called his band, Word, Sound and Power – if anything he was against violence."

Jaffe, the so-called white Wailer – who played harmonica on the Bob Marley & The Wailers album Natty Dread – was in awe of Tosh's musicianship. "They called him 'Peter Touch' because he had an incredible feel and the way he used the guitar, often as a percussion instrument, was unique. He was also an incredible singer – powerful and with perfect pitch – and a brilliant lyricist."

Today, Tosh's message seems to be most keenly received on the continent of Africa, where he remains immensely popular. "Don't care where you come from, as long as you're a black man, you're an African," stated the musician in "African", one of his most important songs.

Now Jamaica too, as it sees an international reggae circuit taking hold of its music culture, is finally laying claim to one of its most difficult sons. It is with some reluctance, says Steffens. "The establishment in Jamaica really, really did not like Peter Tosh. He was considered a crazy man and to this day there's a lot of bitterness towards Peter among the upper class in Jamaica."

He refers to the former Wailer as "the forgotten man". That's now changing. With a biography, a film, an annual symposium and a birthday concert, the man born Winston Hubert McIntosh is receiving new recognition. His family has newly unified and steps are being taken to ensure a lasting legacy. Peter Tosh, the most neglected member of reggae's greatest trio, is finally getting his dues: equal rights and justice.

'The Life of Peter Tosh: Steppin' Razor' by John Masouri is published by Omnibus Press

TOSH: HIS GREATEST HITS

1966

Writes and sings lead vocals on The Wailers' first-ever song about Rastafari – "Rasta Shook Them Up". Tosh was way ahead of Bob Marley and Bunny Wailer in this regard.

1975

"Legalise It" single is banned in Jamaica for advocating the legalisation of marijuana. Tosh prints the lyrics in The Gleaner newspaper and appeals to Prime Minister Michael Manley to lift the ban after handing him a copy signed "from one living legend to another".

1976

Equal Rights album for EMI is hailed as a masterpiece of Afro-centric reggae music. It has since attracted comparisons with the best works of Marvin Gaye and Curtis Mayfield for its revolutionary song content.

1978

Records "Don't Look Back" with Mick Jagger and then supports the Stones on their Some Girls tour. He later appears on Saturday Night Live with Jagger; during the show he sings "Bush Doctor", another ganja anthem, which goes out live on American TV.

BY JOHN MASOURI