The eldest child of 1950s rock 'n' roller Marty Wilde (birth name Reginald Smith) and Joyce Baker, who had been a member of the singing and dancing group the Vernons Girls, Kim Smith was born in the West London suburb of Chiswick and attended Oakfield Preparatory School, in the Southeast London area of Dulwich. When she was nine, the family moved to Hertfordshire, where she was educated at Tewin and later Presdales School. In 1980, at age 20, she completed a foundation course at St Albans College of Art & Design. As Kim Wilde, she was signed to RAK Records by Mickie Most.

Wilde holds the record for being the most-charted British solo female act of the 1980s, with seventeen UK Top 40 hit singles throughout the decade (including her duets with Junior Giscombe and Mel Smith).

Wilde released her debut single "Kids in America" in January 1981. An instant success, it reached number two in the UK Singles Chart and scaled the Top 5 in other countries such as Germany, France and Australia. Although it achieved only moderate success in the US, peaking at number 25 when released in 1982, it is often regarded today as Wilde's signature song. Her debut album Kim Wilde repeated the success of the single, spawning two further hits in "Chequered Love" (Top 5 in the UK, France, Australia and Germany) and the UK-only single "Water on Glass".

Wilde's follow-up album was 1982's Select, led by the hit singles "Cambodia" and "View from a Bridge". Both were number 1 hits in France and reached Top 10 positions in Germany and Australia. At the time, there was some controversy about Wilde's hesitation to do live concerts. Her first concerts in September 1982 took place in Denmark, before embarking on a UK-wide tour in October. Wilde's third album, Catch as Catch Can (1983) was a relative failure. The first single from the album, "Love Blonde", was another success in France and Scandinavia, but failed to have major success in other countries. The failure of the album led to her leaving RAK and signing with MCA Records in the summer of 1984.

Wilde has provided inspiration for other artists, including Charlotte Hatherley, who wrote a song about her entitled "Kim Wilde", and included it on her debut album, Grey Will Fade. East German punk rock band Feeling B also recorded a song called "Kim Wilde", which featured on their debut album. In 1985, French singer Laurent Voulzy paid tribute to Wilde in his song "Les Nuits Sans Kim Wilde" ("Nights Without Kim Wilde"). In her graphic novel Persepolis, Iranian Cartoonist Marjane Satrapi has a comic strip titled Kim Wilde. In it the main character Marji, a young Iranian girl, sings "Kids in America" in the streets of the Iranian capital. Also, when her parents go on holiday in Turkey, they buy a poster of Kim Wilde and smuggle it into Tehran for Marji. Marji pins the poster on her bedroom's wall and practises emulating Wilde.

On her fifth album, 1986's Another Step, Wilde wrote or co-wrote most of the songs. The album's lead single "Schoolgirl" flopped in Europe and Australia, but Wilde's fortunes improved in spectacular fashion with the album's second single, a Hi-NRG remake of The Supremes classic "You Keep Me Hangin' On". After topping the charts in Australia and Canada and peaking at number two in the UK, it became a US number one single in 1987. With that hit, she became the fifth UK female solo Artist ever to top the US Hot 100, following Petula Clark, Lulu, Sheena Easton, and Bonnie Tyler. Her popularity, especially in her native UK, was revitalised and she scored further Top 10 hits in 1987 with "Another Step (Closer to You)" (recorded with Junior) and "Rockin' Around the Christmas Tree" (a Comic Relief charity single, recorded with Comedian Mel Smith).

In 1988, Wilde released her biggest selling album to date, Close, which returned her to the UK top 10 and spent almost eight months on the UK album chart. It produced four major European hits: "Hey Mr. Heartache", "You Came", "Never Trust a Stranger" and "Four Letter Word" (the last 3 were Top 10 hits in the UK). The release of the album coincided with a tour of Europe, where she was the opening act for Michael Jackson's Bad World Tour. Wilde released her next album, Love Moves, in 1990. The album barely made the UK Top 40, and, although it was a Top 10 success in Scandinavian countries, it failed to sell as well as its predecessor and only spawned two minor hits, "It's Here" a Top 20 success in Middle and Northern Europe as well as "Can't Get Enough (Of Your Love)", her last Top 20 hit in France. She toured Europe again, this time opening for fellow Briton David Bowie.

A number of artists have performed covers of Kim Wilde songs, ranging from pop and rock to dance and death metal versions. On February 16, 1991, then Nirvana Drummer Dave Grohl recorded a version of "Kids in America" in an Arlington, Virginia basement studio. It is the third track on the rare 2015 "Songs from the Laundry Room" Foo Fighters EP, a clip of which plays during the credit roll of the Seattle, Washington episode of Grohl's Sonic Highways documentary TV series. American pop star Tiffany recorded a version of "Kids in America" in 2007 for her album I Think We're Alone Now: '80s Hits and More. German eurodance act Cascada, recorded a version of "Kids in America", on their Everytime We Touch album in 2007.

A collaboration with Rick Nowels, who had produced hits for Stevie Nicks and Belinda Carlisle, resulted in the guitar-driven pop of the single "Love Is Holy" and the album Love Is (1992). The album's success was again limited to a small number of countries, though the single became another Top 20 hit in the UK, and the second single ("Heart Over Mind") also made the top 40. In 1993, she released her first official compilation album The Singles Collection 1981–1993, which was a success throughout Europe and Australia and the dancefloor-influenced single "If I Can't Have You" (a cover of the Yvonne Elliman song from the film Saturday Night Fever that was penned by the Bee Gees), became her last UK Top 20 Hit as well as a number 3 hit in Australia.

Wilde embarked on a huge "Greatest Hits" concert tour through Europe in 1994 and also toured Australia and Japan for the first time in six years. Her next album, Now & Forever (1995), was a commercial failure worldwide. Her single "Breakin' Away", however, was a minor hit, and the follow-up, "This I Swear", was also a minor hit in Europe. She released a single "Shame" in 1996. From February 1996 to February 1997, Wilde appeared in London's West End production of the musical, Tommy. After this, Wilde started recording a new album. However, there were problems with her record company – MCA Records had by that time become part of Universal Music – and legal problems concerning the songs. Subsequently, Wilde abandoned the album which remains unreleased.

On 1 September 1996, Wilde married her co-star in Tommy, Hal Fowler, and expressed a Desire to have children as soon as possible. On 3 January 1998 she gave birth to Harry Tristan. On 13 January 2000, Rose Elisabeth was born.

Worldwide, she has sold over 10 million albums and 20 million singles. Starting in 1998, while still active in music, she has branched into an alternative career as a landscape gardener.

In 2001, she (along with fellow horticulturist David Fountain) created the "All About Alice" garden for the Tatton Flower Show and was awarded the 'Best Show Garden' award. In 2005, she won a Gold award for her courtyard garden at the Royal Horticultural Society's Chelsea Flower Show. She has designed and created numerous gardens during her involvement in the Better Gardens and Garden Invaders TV programmes and commissioned by individuals and organisations. She has also created gardens for Flower Shows across the UK and received, with David Fountain, an entry in the Guinness Book of World Records for successfully moving (from Belgium) and replanting the world's largest tree in January 2001. After standing in its new location for six years, however, the tree was toppled by a storm in January 2007.

Since 2003, Wilde has appeared on numerous festival bills and concerts all over Europe with her own band. In early September 2009, a brand new single, "Run to You", recorded as a duet with Swedish rock band Fibes, Oh Fibes!, was released in Sweden. The song reached the Swedish Top 30.

Wilde has written two books as part of her gardening career. The first, Gardening with Children, was released on 4 April 2005 by Collins publishers. Translations of the book were released at the same time in Spain, France, Denmark and the Netherlands, and later in Germany. Her second book, The First-Time Gardener, was released on 3 April 2006 (again by Collins), and is a beginner's guide to gardening.

In 2006, Wilde signed a new record deal with EMI Germany and released the first single from her tenth studio album in many countries across Europe, Scandinavia and Asia. "You Came 2006" charted Top 20 in most of these countries and became her biggest solo hit in Germany since 1988. The album Never Say Never included eight new tracks plus five re-worked previous hits and has charted in Belgium, France, Switzerland, Austria and Germany. The second single from the album, which was voted for by fans on her official website was "Perfect Girl", released in November 2006 and spent nine weeks on the German Top 100 singles chart. A third single, "Together We Belong", was released in March 2007 and a fourth single, "Baby Obey Me", was released in Germany as a remix featuring German Rapper Ill Inspecta.

As of 2008, Kim's brother Marty is a landscape gardener and her sister, Roxanne, is a backing singer for Kylie Minogue.

In 2010, Wilde signed a new record deal with Sony Music Germany. The label released her eleventh studio album, Come Out and Play on 17 August, with "Lights Down Low" preceding that as lead single. The album reached number 10 in Germany and was followed by a tour in Europe in February and March 2011.

Wilde's twelfth studio album, Snapshots, was released on 26 August 2011 and features cover versions of songs hand-picked from the last five decades. A double release of "It's Alright" and "Sleeping Satellite" was released on 19 August as the lead single. Two further singles failed to reach the chart. Kim toured in support of the album in Germany in March 2012. In November 2012, Wilde was featured as the lead vocalist on Reflekt's "A Beautiful House," which can be found on Armada Music's "Antillas & Dankmann's Best Remix 2002-2012" compilation.

Wilde released a new studio album, Wilde Winter Songbook in November 2013.

On 18 December 2017, Wilde released a Christmas single with Lawnmower Deth titled "F U Kristmas"

Wilde released her new album in 2018, “Here Come the Aliens” after having an encounter with a UFO in 2009. While sitting in her garden she noticed something odd about the sky. As she beheld, there was a huge bright light behind a cloud. She curiously walked down the grass to track the source of the light and what she noticed was that the light was swiftly moving back and forth. She thought about it every day and it gave her the idea for her new album.