When Michael Tippett died in 1998, he was widely regarded as the finest British composer of his generation, with the possible exception of Benjamin Britten. More than twenty years on, his reputation in parts of the musical world remains strong. But with some exceptions – such as A Child of our Time, an oratorio that includes negro spirituals – many of Tippett’s more important works are now seldom performed. Alex Ross’s influential The Rest is Noise, a history of classical music in the 20th century, says very little about Tippett.

Hopefully Oliver Soden’s excellent biography, the first written since the composer died, will do something to restore interest in this intriguing figure. Born in 1990, Soden is too young to have met the composer but he has done him proud, reading countless letters and tracking down a huge number of people who knew Tippett.

What matters most about Tippett is the music. This is often contrapuntal and sometimes strikingly dramatic; complex, dancing rhythms contrast with long and lush melodies in slower movements. At its finest moments, the music lifts the heart with an exuberant, life-affirming force.

But Tippett’s life is also of interest, and his responses to the social and political upheavals that he observed often shaped the music. For example, A Child of Our Time is about the murder of a German officer by Herschel Grynszpan, a Jewish boy in Paris; the retribution against the Jews that ensued with Kristallnacht; and the broader implications for humanity.

Three of the questions that intrigue me about Tippett are: why was he such a late developer as a composer; how was he able to go on writing masterpieces when he was in his eighties; and why is so little of his music played today?

On the first question, Tippett was not unique in being a slow starter; Anton Bruckner did not begin to compose till his late thirties. But it is unusual for a great composer to write nothing that he or she subsequently acknowledges before they are 30. And although Tippett decided at 18 to become a composer, he did take a particularly long time to develop. His First String Quartet appeared only in 1935, when he was 30, followed by the First Piano Sonata and the Concerto for Double String Orchestra few years later. He had the self-belief and determination to plug away at composing until he got better.

Soden does not tackle this question directly, but provides many clues. Despite spending a few years at the Royal College of Music, Tippett lacked a musical mentor (of the sort that Britten had with Frank Bridge) and was in many respects self-taught. And when Tippett was a young man he put a lot of his time and energy into organising music in working class communities in both London, running an orchestra at Morley College, and in the North East, where he staged The Beggars’ Opera and his own Robin Hood folk opera in mining villages. He was also busy with politics, enthusing for both pacifism and Trotskyism. Ted Grant, who later founded the Militant tendency, expelled Tippett from a Trotskyist party in 1940, on account of his pacifism and he did time for it in Wormwood Scrubs in 1943. It was during the war that he began to be recognised as a leading composer, and from then on political distractions became less important.

As to the second question, several other composers completed masterpieces when elderly – Verdi wrote Falstaff in his late seventies, and Richard Strauss Four Last Songs in his early eighties. But Tippett finished The Rose Lake, a magical orchestral work, when he was 89, just a few years after the cantata Byzantium and the Fifth String Quartet. Perhaps only Elliott Carter, who was still writing major works in his nineties, outscores Tippett in that respect.

Soden is right to contradict those who have argued that the final phase of Tippett’s career was one of decline. Some of the best work came in the final decades, though as Soden admits, there were disappointments, such as the last two operas. Tippett stopped listening to criticism and seldom revised his final works. But his creative juices kept flowing almost until the end, assisted by his benevolent disposition, generally good health and a supportive network of friends.

The question of why so much of the music is now ex-repertoire is particularly puzzling, given that many of the younger generation of composers, like James MacMillan, acknowledge Tippett’s influence. One possible answer, according to Michael Henderson’s savage review of Soden’s book in The Times, is that Tippett was simply a “mediocrity in an age of giants”. Henderson’s bile seems driven as much by his contempt for the composer’s liberal-left-pacifist personality as any serious attempt to engage with the music. Soden rightly rejects the Henderson thesis. After all, it was Britten who told a BBC producer in 1975: “I am second to none of admiration of [Tippett’s] works and striking personality”.

Soden does address this question and suggests that part of the answer is money. Tippett was a notorious spendthrift and died with large debts. For eight years all the royalties from his works went to the publishers Schott, to pay off debts. Subsequently the royalties have gone to the Michael Tippett Foundation – but the composer’s will stipulated that that trust could only support young composers and musicians; it may not promote Tippett’s own music. The performance of modern music generally requires subsidy, and a well-endowed estate might have been expected to provide that.

Tippett’s music is often not only hard to perform, but also expensive. The Rose Lake, for example, requires an array of some 40 “rototoms” (tuned drums). The Mask of Time, written in the early 1980s, is a two-hour work for soloists, choir and orchestra, which attempts to cover most of human history, and includes some of Tippett’s most dramatic music. One fears that the sheer expense will prevent many performances of this work.

Another problem is that Tippett was his own librettist for operas and choral works, and his words can be off-putting. From the 1960s onwards he tended to put hippy or colloquial speech into libretti, which now sounds dated. Even the not-too-bad libretto of the early 1950s Midsummer Marriage – his first opera, containing Tippett’s most lyrical music – is a strange blend of T S Eliot, Carl Jung and Mozart’s Magic Flute. All that said, Britain’s publicly-funded institutions, such the opera houses and the BBC Proms, could and should do more to foster Tippett performances.

Soden goes into a lot of detail on Tippett’s private life, which earlier biographies, and the composer’s own (thoroughly entertaining) autobiography had glossed over. As a young man Tippett had a number of boyfriends. Then he got into a series of longer-lasting relationships with Wilfred Franks, Douglas Newton, John Minchinton and Karl Hawker. None of these was particularly satisfactory; Tippett often found that the men exploited his generosity, and they all married women. Finally, in 1963 Tippett met Meirion “Bill” Bowen, 35 years his junior, and the pair eventually formed what was by all accounts a happy partnership.

Tippett always wanted a family and tried hard – without success – to have sex with close female friends, as a prelude to marriage. But he sort of got there in the end: Soden tracked down Hawker’s two daughters, Sarah and Susan, who were in some respects brought up by Tippett. They spent a lot of their childhood and young adulthood with the composer, without their parents, and recall his love of fun and games, his charm and constant conversation and their many foreign holidays.

Soden is particularly strong on Tippett’s complex relationship with Britten, nine years his junior. They had much in common, in addition to homosexuality and pacifism, such as their efforts to revive Purcell’s music, their hostility to the stuffy English musical establishment and their openness to new music from other countries. Soden describes the huge respect that each felt for the other, and how their friendship survived the occasional tiff and the sniping of their acolytes. Soden’s book complements Paul Kildea’s fine 2013 biography of Britten, which is also good on their relationship. Tippett always acknowledged Britten’s greater fluency as a composer and wrote after he died: “Britten has been for me the most purely musical person I have ever met and have ever known”.

I would have liked the book to have said more about the musical influences on Tippett; even allowing for the fact that he did not follow or found any school, Soden might have tried to place Tippett somewhere in the history of 20th century music. Nor are we told much about what Tippett thought of important contemporaries, such as Luciano Berio, Olivier Messiaen, Henri Dutilleux, Witold Lutoslawski or even Dmitri Shostakovich. But these are minor quibbles. This readable, informative and fascinating biography, sympathetic without being hagiographical, will be the standard work for a generation and should encourage people to listen to the music.