In 1946, under the name Clementina Dinah Campbell, Laine married George Langridge, a roof tiler, with whom she had a son, Stuart. The couple divorced in 1957. It was not until 1953, when she was 26 and applying for a passport for a forthcoming tour of Germany, that Laine found out her real birth name, due to her parents not being married at the time and her mother registering her under her own name.

She played the lead in a new play at London’s Royal Court Theatre, home of the new wave of playwrights of the 1950s such as John Osborne and Harold Pinter. This led to other stage performances, such as the musical Valmouth in 1959, the play A Time to Laugh (with Robert Morley and Ruth Gordon) in 1962, Boots With Strawberry Jam (with John Neville) in 1968, and eventually to her role as Julie La Verne in Wendy Toye’s production of Show Boat at the Adelphi Theatre in London in 1971. Show Boat had its longest run to date in that London season with 910 performances staged.

During this period, she had two major recording successes. “You’ll Answer to Me” reached the British Top 10 while Laine was “prima donna” in the 1961 Edinburgh Festival production of Kurt Weill’s opera/ballet The Seven Deadly Sins, directed and choreographed by Kenneth MacMillan. In 1964 her Shakespeare and All that Jazz album with Dankworth was well received. Dankworth and Laine founded the Stables theatre in 1970 in what was the old stables block in the grounds of their home. It was an immediate success, with 47 concerts given in the first year.

Laine’s international activities began in 1972, with a successful first tour of Australia, where she released six top 100 albums throughout the 1970s. Shortly afterwards, her career in the United States was launched with a concert at New York’s Lincoln Center, followed in 1973 by the first of many Carnegie Hall appearances. Coast-to-coast tours of the US and Canada soon followed, and with them a succession of record albums and television appearances, including The Muppet Show in 1977. This led, after several nominations, to her first Grammy award, in recognition of the live recording of her 1983 Carnegie concert. She has continued to tour periodically, including in Australia in 2005.

Laine’s relationship with the musical theatre started in Britain and continued in the United States with starring performances in Sondheim’s A Little Night Music and Franz Lehár’s The Merry Widow (Michigan Opera). In 1980 she starred in Colette, a musical by Dankworth. The show began at the Stables theatre, Wavendon, in 1979 and transferred to the Comedy Theatre, London, in September 1980. In 1985 she originated the role of Princess Puffer in the Broadway musical The Mystery of Edwin Drood, for which she received a Tony nomination. In 1989 she received the Los Angeles critics’ acclaim for her portrayal of the Witch in Sondheim’s Into the Woods.

In May 1992, Laine appeared with Frank Sinatra for a week of concerts at the Royal Albert Hall in London.

Laine’s autobiography, Cleo, was published in September 1994 by Simon & Schuster. Her second book, You Can Sing If You Want To, was published by Victor Gollancz in October 1997. In 2000, she appeared as vocalist Gwen in the movie The Last of the Blonde Bombshells.

In the 1997 New Year’s Honours list, Laine became a Dame Commander, and she was appointed Dame Cleo Laine DBE. In the 2006 New Year’s Honours list, her husband was made a knight bachelor, becoming Sir John Dankworth. They were one of the few couples where both partners held their titles in their own right and the only couple in jazz to be thus recognised.

Dankworth died on 6 February 2010, hours before a planned concert at the Stables theatre in Wavendon to celebrate the venue’s 40th anniversary. He had been ill for several months following a concert tour in the United States. Despite her grief, Laine performed at the 40th anniversary concert, along with the John Dankworth Big Band and several members of her family – only announcing his death at the end. Laine’s decision to perform featured on newspaper front pages all over the world, including a full photograph of her on the front page of The Times.

In March 2010, Laine and Dankworth’s final musical collaboration was released on CD and for download – Jazz Matters. The recording featured the Dankworth Big Band playing new compositions written by Dankworth for the couple’s performance at the 2007 Proms at the Royal Albert Hall.