Shirley Bassey was born the last child of Eliza Jane and Henry Bassey in Tiger Bay, Cardiff, Wales, of paternal Nigerian and maternal English heritage. She grew up in the working-class dockside district of Splott, and sang at an early age in the youth choir of the local Salvation Army. After leaving Moorland School at the age of fifteen, Bassey first found employment packing at a local factory while singing in local public houses and clubs in the evenings and weekends. In 1953, she signed her first professional contract, to sing in a touring variety show Memories of Jolson, a musical based on the life of Al Jolson. She next took up a professional engagement in Hot from Harlem, which ran until 1954. By this time Bassey had become disenchanted with show business, and had become pregnant at 16 with her daughter Sharon, so she went back to waitressing in Cardiff. However, in 1955, a chance recommendation of her to Michael Sullivan, a Streatham-born booking agent, put her firmly on course for her destined career. He saw talent in Bassey, and decided he would make her a star. She toured various theatres until she got an offer of the show that put her firmly on the road to stardom, Al Read's Such Is Life at the Adelphi Theatre in London's West End. While she starred in this show, Philips A&R and record producer Johnny Franz spotted her on television, was impressed, and offered her a recording deal. Bassey recorded her first single, entitled "Burn My Candle (At Both Ends)", and Philips released it in February 1956, when Bassey was just nineteen. Owing to the suggestive lyrics, the BBC banned it, but it sold well nonetheless, backed with her powerful rendition of "Stormy Weather". Further singles followed, and in February 1957, Bassey had her first hit with "Banana Boat Song", which reached #8 in the UK Singles Chart. During that year, she also recorded under the direction of American producer Mitch Miller in the US for the Columbia label, producing the single "If I Had a Needle and Thread" b/w "Tonight My Heart She Is Crying". In mid-1958, she recorded two singles that would become classics in the Bassey catalogue. "As I Love You" was released as the B-side of another ballad, "Hands Across the Sea"; it did not sell well at first, but after a chance appearance at the London Palladium things began to pick up. In January 1959, it reached number one and stayed there for four weeks. It thus became the first number one single by a Welsh artist. Bassey also recorded "Kiss Me, Honey Honey, Kiss Me" at this point, and while "As I Love You" raced up the charts, so too did this record, with both songs being in the top three at the same time. A few months later, Bassey signed to EMI's Columbia label, and the second phase in her recording career had begun.

In the early and mid 1960s, Bassey had numerous hits on the UK charts, and five albums in the top 15. Her 1960 recording of "As Long As He Needs Me" from Lionel Bart's Oliver! reached #2, and had a chart run of 30 weeks. In 1962, Bassey's collaboration with Nelson Riddle and his orchestra produced the album Let's Face the Music (#12) and the single "What Now My Love" (#5). Other top ten hits of the period included her second #1, the double A-side "Reach for the Stars"/"Climb Ev'ry Mountain" (1961), "I'll Get By" (also 1961), and a cover version of the Ben E. King hit "I (Who Have Nothing)" in 1963. During this period, John F. Kennedy invited Bassey to sing at his Inaugural Ball.

In 1965, Bassey enjoyed her first U.S. Top 10 chart hit with the title song of the James Bond film, Goldfinger – from the #1 original soundtrack in the U.S. that same year. Owing to the success of Goldfinger, she appeared frequently on many American television talk shows such as those hosted by Johnny Carson and by Mike Douglas. Also in 1965, she sang the title track for the spoof James Bond film The Liquidator, and had a Top 20 live album recorded during a sell-out run at London's Pigalle.

From 1964 onwards the "Goldfinger" single had a lasting impact on her career: writing for the sleeve notes of Bassey's 25th Anniversary Album, Clayton (1978) notes that: "Acceptance in America was considerably helped by the enormous popularity of (Goldfinger)...But she had actually established herself there as early as 1961, in cabaret in New York. She was also a success in Las Vegas...'I suppose I should feel hurt that I've never been really big in America on record since Goldfinger...But, concertwise, I always sell out.'..." This was reflected in the fact that Bassey had only one solo LP to reach the Top 20 in a US chart (R&B, Live at Carnegie Hall), and she was technically a "one-hit wonder," making only one appearance in the Top 40 of the Billboard Hot 100, "Goldfinger". But in the aftermath of "Goldfinger" her UK sales started to falter as well: only two of her singles would enter the top 40 until 1970. She had signed to United Artists, and her first album on that label, 1966's I've Got a Song for You, spent one week on the chart; from there until 1970, only two albums would enter the top 40, one of those a compilation. In 1967 came the release of one of her best-known singles "Big Spender", although it charted just outside the UK Top 20.

Bassey started living as a tax exile in 1968, and was not permitted to work in Britain for almost two years. Also in 1968, at the Sanremo Festival in Italy, she performed "La vita", an Italian song by Bruno Canfora and Antonio Amurri, with some lyrics re-written in English by Norman Newell for her performance. Her version of the song with chorus sung in Italian became a Top 40 hit on the Italian chart, and Bassey recorded several songs in Italian, some appearing on a 1968 Italian album titled La vita. (Later, Newell would write English lyrics for the rest of "La vita", and the result was "This Is My Life".) But her UK sales continued to suffer.

Bassey's UK comeback came in 1970, leading to one of the most successful periods of her career. In this year, she returned to the UK with a record breaking run of performances at the Talk of the Town nightclub. Also in that year, she released the album Something, which showcased a new Bassey style, a shift from traditional pop to more contemporary songs and arrangements (the single of the same name was more successful in the UK charts than the original Beatles recording - the only artist to have achieved this), though Bassey would never completely abandon what had been her forte, standards, show tunes, and torch songs. "Something" was also a Top 10 U.S. hit on the Adult Contemporary chart. Other singles of this period included top ten hits "For All We Know" (1971) and "Never Never Never" (1973) – the latter also reaching the Top 10 in the U.S. Adult Contemporary Chart. The success of "Something" (single #4, album #5) spawned a series of successful albums on the UA label, including Something Else (1971), And I Love You So (1972), I Capricorn (1972), Never Never Never (1973), Good, Bad but Beautiful (1975), Life, Love and Feelings (1976), You Take My Heart Away (1977) and Yesterdays (1978). Bernard Ighner wrote and duetted with Bassey for the track "Davy" on the Nobody Does It Like Me album (1974). Additionally, two of Bassey's earlier LPs entered the charts, 1967's And We Were Lovers (re-issued as Big Spender), and 1962's Let's Face the Music (re-issued as What Now My Love). Two compilations, The Shirley Bassey Singles Album (1975) and 25th Anniversary Album (1978) both made the UK top three: The Shirley Bassey Singles Album her highest charting album at No. 2 and earning a gold disc, and 25th Anniversary Album going platinum.

Between 1970 and 1979, Bassey had 18 hit albums in the UK Albums Chart. Her 1978 album The Magic Is You featured a portrait by the photographer, Francesco Scavullo. In 1973, her sold-out concerts at New York's Carnegie Hall were recorded and released as a two-LP set, Shirley Bassey: Live at Carnegie Hall. This album and the majority of her recordings from this period have been re-mastered and released on CD by EMI and BGO Records. In 1971, she recorded the theme song for Diamonds Are Forever. The recording featured as part of Sydney, Australia's 2007 New Year's celebration.

Bassey appeared on the Morecambe and Wise Christmas Show, broadcast on Christmas Day in 1971. In 1976 Bassey starred in the six-episode The Shirley Bassey Show, the first of her television programs for the BBC, followed by a second series of six episodes in 1979. The final show of the first series was nominated for the Golden Rose of Montreux in 1977. The series featured guests including Neil Diamond, Michel Legrand, The Three Degrees and Dusty Springfield; filmed in various locations throughout the world as well as in the studio.

In 1978 Bassey pleaded guilty to being drunk and disorderly "after shouting abuse in the street and pushing a policeman".

Bassey closed out the decade with her third title theme for the Bond films, Moonraker (1979).