Lionel Bart [formerly Begleiter], song-writer and composer of musicals, was born on 1 August 1930 at 24 Underwood Road in the East End of London to a Jewish family, the youngest of the eleven children of Morris Begleiter, a master tailor, and his wife, Yetta, née Darumstundler (1883/4–1970), both of whom had fled persecution in Polish Galicia. Bart's musical talent was noted as a child, although he did not receive any formal musical education and never learned to read music. At the age of sixteen Bart went to St Martin's School of Art, London, to study painting. However, he felt uncomfortable with the solitude of a painter's life, and developed an interest in community theatre. His musical and theatrical sensibilities were shaped by his early involvement in the left-leaning International Youth Centre (IYC) and his membership of the Communist Party. From 1952 he staged cabarets for the IYC, wrote political songs, and gained his love for improvisation. His work was, and continued to be, steeped in the music-hall tradition and suffused with a strong sense of working-class identity.

Bart was talent-spotted by the actor Alfie Bass, who was running the Unity Theatre (a left-leaning theatre located near King's Cross), and heard a Bart song called ‘Turn It Up’. For the Unity, Bart wrote Piecemeal—an agit-prop version of the Cinderella story—and his first real musical, a take-off of Ben Jonson's Volpone entitled Wally Pone, King of the Underworld. He changed his name from the Jewish Begleiter to the more anglophone Bart, taken from St Bartholomew's Hospital, which he passed on his journey from the East End to the Unity Theatre.

Bart's work brought him to the attention of Joan Littlewood, the director of the Theatre Royal, Stratford East, London. His collaboration with Littlewood brought him to prominence with the successful staging in 1959 of his first full-length musical, Fings ain't wot they used to be, based on the book by the former villain Frank Norman, which enjoyed a two-year run. Its storyline of aspiring Soho villains and teddy boys mirrored the changes within working-class culture during a period of dramatic reconstruction: ‘They've changed our local palais into a bowling alley and fings ain't wot they used to be.’

In the mid-1950s Bart began a successful career as a song-writer with Tommy Steele, with whom his hits included ‘Rock with the Caveman’, ‘A Handful of Songs’, ‘Water, Water’, and ‘Little White Bull’. He also wrote a variety of hits for other artists such as ‘Do you Mind?’ for Anthony Newley, and won several Ivor Novello awards for song writing. His most famous pop song was ‘Living Doll’, written for Cliff Richard—the first million-selling single in Britain.

Bart's song-writing blended simple lyrics with catchy melodies. Following these successes he attracted the attention of Bernard Miles at the Mermaid Theatre, and wrote his second full-length musical, Lock up your Daughters (1959), a modern version of Henry Fielding's Rape upon Rape. His adaptation the following year of Charles Dickens's novel Oliver Twist into the musical Oliver! seamlessly combined his love of music-hall, Jewish folk themes, and lyrical style with his interest in social justice. Bart was unable initially to attract backers, who felt that the material was too dark, so he gambled with his own money to stage the show. Finally, the impresario Donald Albery took an option after hearing a tape of Bart's friends playing the parts.

The show was a spectacular success and enjoyed extensive West End and Broadway runs, making a star of Ron Moody in the role of Fagin. Oliver! proved to be Bart's greatest legacy, enjoying many professional and amateur revivals (it remains a particular favourite for schools), winning Tony awards, and spawning a multi-Oscar-winning film directed by Sir Carol Reed in 1968. The show featured many catchy anthems including ‘Consider Yourself’, ‘Who will Buy’, ‘Pick a Pocket’, ‘Food Glorious Food’, and ‘As Long as He needs Me’.

The success of Oliver! led to Bart becoming one of the leading figures within the British entertainment world of the early 1960s. In his professional life he was sustained by the relative success of the follow-up musicals Blitz! and Maggie May. Bart further enhanced his reputation as a song-writer when he wrote the first James Bond theme tune—for the film From Russia with Love—which was an international hit for the singer Matt Monro.

Bart also became one of the pivotal figures of swinging London. He entered Princess Margaret's showbiz circle, befriended the Beatles and the Rolling Stones, and became as famous for his houses and castles, parties, drinking, and drug use as for writing music. He indulged in extensive largess: a bowl containing £1000 in notes rested on the mantelpiece of his Fulham palace, from which anyone in need could help themselves. Many obliged. During this period, although openly homosexual within the theatrical world, he was proposed to by Judy Garland, and by Alma Cogan on national television.

Bart's professional fortunes declined in the second half of the 1960s. The musical Twang!! (1965) was a disastrous parody of the Robin Hood myth with a cast including Barbara Windsor as a nymphomaniac Maid Marian and Ronnie Corbett as one of the merry men. JBart's confidence in the show led him to gamble, as he had with Oliver!, by pouring in his own money. To facilitate this he made surely the most disastrous business decision in post-war British theatre by selling the rights to Oliver!, thereby losing—by his own later estimate—over £100 million in royalties on the show's subsequent revivals.

After declaring bankruptcy in 1972, Bart was inactive and descended into alcoholism. His talent for self-destruction was apparent from his speech after the first night of a show entitled Lionel, written by Barry Fantoni and John Wells to showcase his hits. This might have revived his fortunes, but he damned the production and it closed within weeks. In the 1980s he developed a major liver complaint and diabetes, brought on by alcohol abuse. Subsequently he stopped drinking and moved to humbler surroundings in a small flat above a shop in Acton, west London.

In the mid- to late 1980s Bart enjoyed a revival which was orchestrated by the re-release of a comic version of ‘Living Doll’ by Cliff Richard and the Young Ones in 1986. In 1989 he was commissioned to write ‘Happy Endings’ for an award-winning Abbey National advertisement. In 1994 the theatrical impresario Sir Cameron Mackintosh successfully revived Oliver! with Bart's involvement. In a gesture of respect Mackintosh set aside a small amount of the show's profits for its writer. Following this there were smaller-scale revivals of Maggie May, Blitz!, and Fings ain't wot they used to be.

Lionel Bart was diagnosed with cancer, and died on 3 April 1999 at Hammersmith Hospital, London. Despite his apparently humble later lifestyle, he left £1,299,856 in his will to family and friends.