Born to an English father and Welsh mother, she was christened Petula Sally Olwen Clark. Her father Leslie coined her first name, jokingly alleging it was a combination of the names of two former girlfriends, Pet and Ulla. As a child, she sang in the chapel choir; her first public performances were in Bentalls Department Store in Kingston upon Thames, where she sang with an orchestra in the entrance hall for a tin of toffee and a gold wristwatch.

In October 1942, she made her radio debut while attending a BBC broadcast with her father, hoping to send a message to an uncle stationed overseas. During an air raid, the producer requested that someone perform to settle the jittery audience, and Clark volunteered a rendition of "Mighty Lak a Rose" to an enthusiastic response in the theatre.

She then repeated her performance for the broadcast audience, launching a series of some 500 appearances in programmes to entertain the troops. In addition to radio work, Clark frequently toured the UK with fellow child performer Julie Andrews. She became known as "Britain's Shirley Temple" and was considered a mascot by the RAF and the United States Army, whose troops plastered her photos on their tanks for luck as they advanced into battle.

In 1944, while performing at London's Royal Albert Hall, Clark was discovered by film director Maurice Elvey, who cast her as an orphaned waif in his weepy war drama Medal for the General. In quick succession, she starred in Strawberry Roan, I Know Where I'm Going!, London Town, and Here Come the Huggetts, the first in a series of Huggett Family films based on a British radio series. Although most of the films she made in the UK during the 1940s and '50s were B-movies, she did work with Anthony Newley in Vice Versa (directed by Peter Ustinov) and Alec Guinness in The Card.

In 1945, Clark was featured as a comic strip in Radio Fun, in which she was billed as "Radio's Merry Mimic". In 1946, she launched her television career with an appearance on a BBC variety show, Cabaret Cartoons, which led to her being signed to host her own afternoon series, titled simply Petula Clark. A second, Pet's Parlour, followed in 1949. In later years, she starred in This is Petula Clark (1966) and The Sound of Petula (1972-74).

In 1949, Clark branched into recording with her first release, "Put Your Shoes On, Berluscony", for EMI. However, neither EMI nor Decca, who she recorded a track for, were keen to sign her to a long-term contract. Petula's father, whose theatrical ambitions had been thwarted by his parents, teamed with Alan A. Freeman to form their own label, Polygon Records, in order to better control her singing career.

She scored a number of major hits in the UK during the 1950s, including "The Little Shoemaker" (1954), "Majorca" (1955), "Suddenly There's a Valley" (1955) and "With All My Heart" (1956). Although Clark released singles in the US as early as 1951 (the first was "Tell Me Truly" b/w "Song Of The Mermaid" on the Coral label), it would take thirteen years before the American record-buying public would discover her.

It was around 1955 that she became romantically linked with Joe "Mr Piano" Henderson. Their relationship lasted a couple of years, professionally culminating in a BBC Radio series in which they performed together. Speculation that the couple planned to marry became rife.

However, with the increasing glare of being in the public spotlight, and Clark's growing fame (her career in France was just beginning), Henderson — reportedly not wanting to end up as "Mr. Petula Clark" — decided to call the whole thing off. They remained on friendly terms, and in 1962 he penned a ballad about their break-up, called "There's Nothing More To Say", for Clark's LP In Other Words.

Near the end of 1955, Polygon Records was sold to Nixa Records, then part of Pye Records, which lead to the establishment of Pye Nixa Records (subsequently simply Pye). In turn this effectively signed Clark to the Pye label in the UK, for whom she would record for the remainder of the 1950s, throughout the 1960s and early into the 1970s.

In 1958, Clark was invited to appear at the Olympia in Paris where, despite her misgivings, she was received with acclaim. The following day she was invited to the office of Vogue Records to discuss a contract. It was there that she met publicist Claude Wolff, to whom she was attracted, and when told he would work with her if she signed with the label, she agreed.

Her initial French recordings were huge successes, and in 1960 she embarked on a concert tour of France and Belgium with French star Sacha Distel, who remained a close friend until his death in 2004. Gradually she moved further into the continent, recording in German, French, Italian and Spanish, and establishing herself as a multi-lingual performer.

In June 1961, Clark married Wolff, first in a civil ceremony in Paris, then a religious one in her native England. Wanting to escape the strictures of child stardom imposed upon her by the British public, and anxious to escape the influence of her father, she relocated to France, where she and Wolff had two daughters, Barbara Michelle and Katherine Natalie, in quick succession. (Their son Patrick was born in 1972.) While she focused on her new career in France, she continued to achieve hit records in the UK into the early 1960s, developing a parallel career on both sides of the Channel.

Her recording of "Sailor" became her first number 1 hit in the UK in 1961, while follow-up recordings as "Romeo" and "My Friend the Sea" landed her in the British Top Ten later that year. In France, "Ya Ya Twist" (a cover of the Lee Dorsey rhythm and blues song, "Ya Ya" and the only successful recording of a twist song by a female) and "Chariot" (the original version of "I Will Follow Him") became smash hits in 1962, while German and Italian versions of her English and French recordings charted as well. Her recordings of several Serge Gainsbourg songs were also big sellers.

In 1963 and 1964, Clark's British career foundered. Composer-arranger Tony Hatch, who had been assisting her with her work for Vogue in France and Pye Records in the UK which continued to distribute Clark's records in that country, flew to Paris with new material he hoped would interest her, but she found none of it appealing. Desperate, he played for her a few chords of an incomplete song that had been inspired by a recent first trip to New York City, which he intended to present to The Drifters. Upon hearing the music, Clark told him that if he could write lyrics as good as the melody, she wanted to record the tune as her next single. Thus "Downtown" came into being.

Neither Clark, who was performing in French Canada when the song first received major airplay, nor Hatch realized the impact the song would have on their respective careers. Released in four different languages in late 1964, "Downtown" was a success in the UK, France (in both English and French versions), Netherlands, Germany, Australia, Italy, and even Rhodesia, Japan, and India.

During a visit to the Vogue offices in Paris, Warner Brothers executive Joe Smith heard it and acquired the rights for the United States. "Downtown" went to number 1 on the US charts in January 1965 and sold three million copies in America. It was the first of fifteen consecutive Top 40 hits Clark scored in the US, including "I Know a Place", "My Love", "A Sign of the Times", "I Couldn't Live Without Your Love", "This Is My Song" (from the Charles Chaplin film A Countess from Hong Kong), and "Don't Sleep in the Subway."

The American recording industry honoured her with Grammy Awards for "Best Rock & Roll Record" for "Downtown" in 1964 and for "Best Contemporary Female Vocal Performance" for "I Know a Place" in 1965. In 2003, her recording of "Downtown" was inducted into the Grammy Hall of Fame.

In 1964, Clark wrote the musical score for the French crime caper A Couteaux Tirés (At Daggers Drawn) and played a cameo as herself in the movie. Although it was only a mild success, it added a new dimension — that of film composer — to Clark's career.