Caroline Esmeralda van der Leeuw was born in Amsterdam on April 26, 1981, to a Dutch father and an Aruban mother. She began singing lessons at twelve with James Gilloffo and, under his guidance, joined the girl vocal group Les Elles. She also sang with the Philharmonic Funk Foundation, a large Amsterdam funk orchestra, and then trained as a jazz vocalist at the Amsterdam Conservatory, graduating in 2005. For most of her career she has performed in English, and for thirteen years she did it under the stage name Caro Emerald, which is how most listeners know her.

The record that made her famous began as a demo. In early 2007 the producer Jan van Wieringen asked her to sing on a track he was making with the producer and songwriter David Schreurs. "Back It Up," written by Schreurs and the Canadian lyricist Vince Degiorgio over a hip-hop beat by Robin Veldman and van Wieringen, found its audience online and on radio even though publishers and labels passed on it. The four of them then set out to write a concept album with her as the starring artist. The writing began in the summer of 2008 and drew on 1940s and 1950s jazz, easy listening, orchestral Latin music and mambo, set against modern beats. The reference points she and her collaborators have cited include the organist Jackie Davis, the exotica composer Martin Denny, the mambo bandleader Perez Prado, and the vocal example of the Andrews Sisters, Billie Holiday and Sarah Vaughan. Schreurs and Degiorgio were credited as creative directors, she co-wrote several of the songs, and she is credited with the vocal arrangements. With no label willing to sign the project, Schreurs started Grandmono Records to release it.

"Back It Up" came out on July 6, 2009 and peaked at No. 12 on the Dutch Top 40. The follow-up, "A Night Like This," was released in December 2009 and reached No. 1 in the Netherlands in January 2010, and the album Deleted Scenes from the Cutting Room Floor appeared that same month. It debuted at No. 1 in the Netherlands and spent 30 non-consecutive weeks there, passing the 26 weeks Michael Jackson's Thriller had held in 1983, and it eventually reached six-times platinum in her home country. A live EP from the period, Live in the Netherlands, carries two songs recorded at the North Sea Jazz Festival in 2010. The album followed in 2011 across Europe, reaching No. 4 in the United Kingdom and No. 5 in Germany, and its songs were placed in television series and advertising, among them The Vampire Diaries and Agent Carter. She appeared on Jools Holland's Hootenanny on New Year's Eve 2011, and Live in Concert at the Heineken Music Hall, recorded with the Grandmono Orchestra, came out in 2011. Her Dutch honors for 2010 included an Edison Award for best female singer, and she later collected a Goldene Kamera in 2012 and an Echo for best international newcomer.

The second album, The Shocking Miss Emerald, was released on May 3, 2013 and reached No. 1 in both the Netherlands and the United Kingdom, where it also topped the jazz and blues albums chart. Its singles included "Tangled Up," co-written with Guy Chambers, and "Liquid Lunch," BBC Radio 2's Record of the Week. The introduction was credited to Jules Buckley, who became chief conductor of the Metropole Orkest that August. In April 2014 six of its songs were reworked in an acoustic setting for a Record Store Day vinyl EP built around upright bass, guitar and light percussion. On June 29, 2014 she played at Glastonbury.

A quieter stretch followed. "Quicksand" appeared in 2015, the exotica-flavored EP Emerald Island in March 2017, and in December 2017 the EP MO x Caro Emerald by Grandmono, which sets her songs against the Metropole Orkest, the Dutch ensemble that keeps a jazz rhythm section alongside a pop one. She sang at the Leverkusener Jazztage on November 11, 2017. "Wake Up Romeo" in June 2020 was her first new single in three years.

In 2022 she stepped away from the Caro Emerald name. On August 23, 2022 she was revealed as the voice behind The Jordan, whose debut album Nowhere Near the Sky came out on February 10, 2023 on Cooking Vinyl, with a sound far from the vintage jazz of her earlier records. In February 2026 she announced her return under the single name Caro and released "I Can't Win" on February 27. Her album Returning to Innocence, fourteen tracks on Big Mouse that is presented as her most personal work, was released on October 9, 2026. Ronnie Scott's club in London has listed her for two performances on November 28, 2026, which will be her first appearance at the club.

Van der Leeuw is a pop singer with a jazz singer's training, and the two sides are plainly audible in her best-known work. As Caro Emerald she built her sound on a sample-based approach with live instruments, setting the phrasing of 1940s and 1950s vocal jazz and the colors of exotica and Latin orchestral pop against hip-hop and electronic beats, which is why her records are filed under jazz pop and electro swing as often as under jazz. Her own cited vocal models are Billie Holiday and Sarah Vaughan, alongside the close-harmony tradition of the Andrews Sisters. Critics at the time heard the same split: The Independent's Simon Price praised the second album's blend of vintage jazz and modern hip-hop, and the BBC's Lloyd Bradley wrote warmly of the first. She is not a working improviser or a bandleader in the jazz sense, and her songs were written and produced by a small studio team rather than assembled by a jazz rhythm section. Her later work as The Jordan and as Caro is alt-pop with no jazz idiom at all. What keeps her inside the jazz-adjacent circle is the schooling, the repertoire models behind the Caro Emerald records, the jazz festival stages she has played, and the orchestral and acoustic reworkings of those songs.