In 1994, Brown, along with Mel C, Geri Halliwell, and Victoria Beckham responded to an advertisement in The Stage magazine. Around 400 women who answered the advertisement attended auditions at Danceworks Studios in Mayfair, London. Halliwell, Chisholm, Beckham, Brown and Michelle Stephenson were originally chosen as the members of the group which was known as Touch. When Stephenson left she was replaced by Emma Bunton. The group felt insecure about the lack of a contract and were frustrated by the direction in which Heart Management was going and broke with them. In 1995, they toured record labels in London and Los Angeles and after teaming up with music manager Simon Fuller they signed a deal with Virgin Records and the group name is changed to Spice Girls. Their debut album, Spice, was a huge worldwide commercial success, peaked at number one in more than 17 countries, and was certified multi-platinum in 27 countries. The album centred on the idea of Girl Power, and was compared to Beatlemania. In total the album sold 30 million copies worldwide and became the biggest-selling album in music history by a girl group and one of the most successful albums of all time. The first single, “Wannabe”, reached number one in 37 countries and all the following singles – “Say You’ll Be There”, “2 Become 1”, “Who Do You Think You Are” and “Mama” – also peaked at number one in United Kingdom.

From 1996 to 1997, Brown dated Icelandic businessman Fjölnir Thorgeirsson.

In 1997, they released their second album, Spiceworld, and their first two singles “Spice Up Your Life” and “Too Much”, entered the UK Albums Chart at number one, making seven consecutive number one hit singles, an all-time record for a musical group. The album was a global best seller, selling 20 million copies worldwide. The group also starred in their own film, Spiceworld: The Movie, which grossed $100 million worldwide and became the second most watched movie of the year. The next single, “Stop”, peaked at two, breaking the sequence of number ones. “Viva Forever”, another number one, was the last single before Geri Halliwell’s departure from the group in May 1998. As a four-piece, the group released “Goodbye” in late 1998. It topped the UK Singles Chart and became their third consecutive Christmas number-one – equaling the record previously set by The Beatles. Before the split of the Spice Girls, Brown went on to release music with Virgin Records, the label she was signed to when a member of the Spice Girls. “I Want You Back” charted at number 1 on the UK Singles Chart, and also had success around the globe. The song was recorded for the soundtrack of the film Why Do Fools Fall in Love. The single sold 218,000 copies and became the 82nd Bestselling British Single of the year. Due to its futuristic aesthetic in green and black, the video of “I Want You Back” becomes cult, marks the spirits and is considered one of the most beautiful music video of the last three decades.

In March 1998, Brown began a relationship with Dutch dancer Jimmy Gulzar while on the Spiceworld Tour. The couple became engaged on 13 May 1998, Brown became pregnant that June, and the couple were married in Little Marlow, Buckinghamshire, on 13 September 1998. Brown changed her stage name to Melanie G while they were married. Their daughter, Phoenix Chi Gulzar, was born on 19 February 1999. Brown filed for divorce in 2000, and the divorce was finalised later that year. Brown won custody, and paid a settlement of £1.25m to Gulzar. Gulzar was prosecuted for threatening Brown and attacking her sister Danielle. In August 2001, Gulzar was found guilty of the assault, but later cleared by the court.

In 1999, while recording her album, Brown worked with producers such as Sisqó, Teddy Riley, and Jimmy Jam and Terry Lewis (Janet Jackson, Prince), with whom she was also working on the Spice Girls’ third album, Forever. At the suggestion of her then-husband Jimmy Gulzar, Brown covered Cameo’s 1986 hit “Word Up” as her next solo release. The track was already released on the soundtrack to Austin Powers: The Spy Who Shagged Me. The song charted poorly, peaking at fourteen on the UK Singles Chart making it the lowest-charting Spice Girls-related single of the 90s. Turning to television work, she hosted Pure Naughty, a weekly BBC2 magazine show focusing on black music. She also hosted the MOBO Awards on two occasions, in 1998 with Bill Bellamy and in 1999 with Wyclef Jean, and took part in a BBC-funded short film entitled Fish. She hosted a number of TV shows such as This Is My Moment (a talent show) for ITV1 and shot a documentary called Voodoo Princess for Channel 4. She took part in smaller projects as a presenter such as Top of the Pops, Party in the Park for The Prince’s Trust and The All Star Animal Awards. She has appeared as herself in an advert for the Yorkshire tourist board in a series which included contributions from other Yorkshire-born celebrities, and in the film Happy Birthday Oscar Wilde.

Brown’s debut album, Hot was released in October 2000, a month before the final Spice Girls album, Forever was released. Following the release of Forever, which was far less successful than their previous two albums, the Spice Girls stopped recording and the members began investing more time into their solo careers. The lead single from the Hot, “Tell Me”, debuted at No. 4 in the UK charts with about 40,000 copies sold in its first week of release. It sold approximately 100,000 copies, making it the 158th “best seller” of 2000. Further singles were released in February 2001; “Feels So Good” which had peaked at No. 5, followed by a “Lullaby”, a pop number dedicated to her daughter. It was accompanied by a video shot in Morocco and featured Brown with Phoenix Chi. The media criticised Brown for using her child in the music video and single artwork, labeling her Desperate Spice and insinuating that she was exploiting her child as a marketing tool. The single entered and peaked at No. 13. The album was not a success and garnered mediocre reviews, selling a disappointing 7,419 copies in its first week and charting at a weak No. 28 leading to Virgin dumping Brown from their label. In 2002, Brown released her autobiography, Catch a Fire, which reached No. 7 in the official books chart, and saw her touring the UK to promote it with a run of book signings. In 2003 Brown’s first movie role came in the form of a British drama, Burn It. She appeared in a horror film entitled, LD 50 Lethal Dose, which was released directly to DVD in 2005. She acted in a long run of shows as part of the cast for The Vagina Monologues. She was in the movie The Seat Filler, co-produced by Will Smith and starring Destiny’s Child star Kelly Rowland. In April 2004, Brown was approached to take part in the musical Rent as Mimi Marquez In Netherlands.

In 2000, Brown began a relationship with actor Max Beesley; the couple dated for two years.

After Rent, Brown became interested in recording new songs. Since her breakup with Virgin in 2001, she remained distant from music, not interested in a return. She had a leading role in the thriller Telling Lies, and decided to release them a year later through an independent label, Amber Café. The only single from the album, “Today”, saw a UK release in June 2005. “Today” entered the singles chart at No. 41, selling around 1,000 copies in its first week. The album, LA State of Mind, was released on 27 June 2005 in two formats: as a regular CD and as a limited edition with a 30-minute DVD documentary detailing Brown’s life in Los Angeles. In a scathing review, AllMusic stated that this album was one of the worst pop albums of the decade. The album was also released with a bonus DVD featuring an in-depth documentary filmed and directed by Mark McConnell. Brown said she did not sign with a major label because the album was a non-commercial project. She also shied away from recording in an R&B or hip hop style again, instead focusing on using adult themes and rhythms such as in acoustic music following an appearance in the film Love Thy Neighbor.

From 2002 to 2006, Brown was in a relationship with film producer Christine Crokos. Brown and Crokos lived together in Los Angeles, California. Speaking to Gay Star News about the relationship, she said: ‘It wasn’t experimentation. I fell in love with a woman for five years. An experiment doesn’t last five years.’ Asked about the relationship, Brown said: “People call me lesbian, bisexual or heterosexual, but I know who’s in my bed and that’s it. I have a huge libido and a great sex life.” Brown and Crokos’s relationship ended in 2006. Brown said that she had a four-year relationship with a woman when she was in her teens. In 2019, Brown confirmed rumours that she and Geri Halliwell had sex during the height of the Spice Girls’ fame. She said: “It just happened, and we just giggled at it and that was it.”

In September 2007, Brown joined the fifth season of the US television dance competition, Dancing with the Stars with her partner Maksim Chmerkovskiy. On 27 November 2007, they took second place in the show, losing to Hélio Castroneves and his partner, Julianne Hough. That year, the Spice Girls re-grouped and announced plans for a reunion tour, from which they were said to have earned £10 million each (approximately $20 million). The band said that they are still enjoying doing their “own thing”. The group decided to release their first compilation album, Greatest Hits, in early November 2007 and the tour began on 2 December 2007. During one Spice Girls performance at London’s The O2 Arena, the band’s children, including Brown’s children accompanied her on stage during “Mama”, along with the other Spice Girls’ children. During the reformation filmmaker Bob Smeaton directed an official film of the tour entitled Spice Girls: Giving You Everything. As well as their sell-out tour, the Spice Girls were contracted to appear in Tesco advertisements, for which they were paid £1 million each. After splitting for a second time the Spice Girls once again reunited for a special performance at the 2012 London Olympics closing ceremony in August 2012 where they performed “Wannabe” and “Spice Up Your Life”.

Brown became the subject of tabloid stories during her relationship with Hollywood actor Eddie Murphy, who fathered Brown’s second child, Angel Iris Murphy Brown, born 3 April 2007. By early December 2006, Brown and Murphy had separated. Murphy told a journalist that the parentage of Brown’s unborn baby could not be proven until a paternity test was performed. On 22 June 2007, a court-ordered DNA test confirmed that Murphy was the child’s father. Murphy admitted paternity and indicated that he and Brown had reached a paternity settlement of $7 million.

In February 2007, Brown began dating Stephen Belafonte. The couple secretly married on 6 June 2007 in Las Vegas, Nevada, US at A Special Memory Wedding Chapel. They renewed their vows in front of their families on 8 November 2008 in Hurghada, Egypt. On 1 September 2011, Brown gave birth to her third daughter, Madison Brown Belafonte.

In April 2009, Brown joined actress and former Dancing with the Stars champion Kelly Monaco as original stars of a Las Vegas revue called Peepshow at the Las Vegas Planet Hollywood Hotel and Casino. On 17 August 2009, Brown was announced as a visiting panellist on ITV1’s daily lunchtime show Loose Women. She appeared for a week of shows during September 2009. In January 2010, Brown was selected to replace Marissa Jaret Winokur as the new host of Oxygen’s weight loss show Dance Your Ass Off. In September 2010, her own reality show aired on the Style Network called Mel B: It’s a Scary World. In November 2010, the virtual computer game Get Fit with Mel B, was released in North America and Europe. Brown served as a celebrity mentor on the second season of the Australian version of The X Factor during week 8 of the live shows in 2010. During the results show, she performed a duet with the remaining five acts singing “Stop” originally by the Spice Girls. In April 2011, it was announced that Brown would replace Kyle Sandilands as a judge for the third series of the Australian version of The X Factor alongside Ronan Keating, Guy Sebastian and fellow new judge Natalie Bassingthwaighte (who replaced Natalie Imbruglia). For her first series on the show, she was given the Girls category. In February 2012, Brown was announced to replace Sonia Kruger as co-host on the Australian version of Dancing with the Stars. In February of that year, rumours circled of a Spice Girls reunion. Brown revealed that the band were working on some projects for later in the year, including a musical featuring their back catalogue. On 31 March, it was announced that Brown signed a global partnership with EMI Music Australia for the release of her third studio album, but she later broke from the contract.

Brown returned for the fourth series of The X Factor and mentored the Boys category. Her act Jason Owen reached the final, but finished in second place after losing out to Samantha Jade, mentored by Guy Sebastian. In June 2012, it was confirmed that Brown would become a guest judge for the Manchester auditions of the British version of The X Factor alongside Louis Walsh, Gary Barlow and Tulisa Contostavlos.

In July 2012, Brown reunited with the Spice Girls for a one-off performance at the 2012 Summer Olympics Closing Ceremony in London, performing a medley of their hits “Wannabe” and “Spice Up Your Life”. The performance was the most tweeted moment of the entire Olympics with over 116,000 tweets on Twitter per minute. Later in the year, the Spice Girls reunited again to launch and attend the premiere of Viva Forever!. In addition to the promotion of the musical, the group appeared in the documentary, Spice Girls’ Story: Viva Forever! which aired on 24 December 2012 on ITV1.

In March 2013 it was confirmed that Brown would judge Australia’s Got Talent along with Dawn French. The same month, it was confirmed that Brown would not return as a judge for the fifth season of The X Factor due to her commitments with Australia’s Got Talent. Brown was replaced by Dannii Minogue. On 9 April 2013, the Australian Associated Press reported that Brown was off the chain and banned from judging on Australia’s Got Talent after Seven, the Australian TV network that airs The X Factor, filed suit to prevent Brown from appearing on any rival networks. The judge ruled that Brown was still under contract with Seven until January 2014, thus preventing her from appearing on a program aired by another network until after that date. The Nine Network confirmed rumours on 29 April that they had hired former Spice Girl Geri Halliwell to replace Brown.

She had a small part in the final episode of the ITV2 drama series Secret Diary of a Call Girl. In 2013, she returned to acting in the Lifetime movie Twelve Trees of Christmas. From August to September 2013, she became a judge on the televised dancing show, Stepping Out, alongside choreographers Wayne Sleep and Jason Gardiner. That month, Brown released her first single in eight years, “For Once in My Life”, from her untitled and unreleased third studio album. The single peaked at No.2 on the Billboard Hot Dance Club Songs charts.

On 20 February 2013, NBC had announced that Brown would be a judge on America’s Got Talent for its eighth season, alongside Howie Mandel, Howard Stern, fellow new judge Heidi Klum, and eventually Simon Cowell, who replaced Stern in 2016. Brown had replaced Sharon Osbourne. She judged seasons 8 through 13, and the first season of America’s Got Talent: The Champions before her departure was announced in February 2019 and replaced by Gabrielle Union.

In late 2014, she appeared on The Big Fat Quiz of the Year and a sketch with the cast of Coronation Street for charity telethon Text Santa.

Early 2014, Brown become a coach on the Australian version of The Voice Kids, alongside singers Joel Madden and Delta Goodrem. In June, she was confirmed as the fourth judge for the eleventh series of the British version of The X Factor, replacing Nicole Scherzinger. Emma Bunton joined her in Cancun, Mexico for the judges’ houses stage of The X Factor. In December 2014, it was announced that Brown would miss The X Factor final due to illness. In the same year, Brown became a guest co-host on the Breakfast program of Sydney radio station 2Day FM, alongside Jules Lund, Merrick Watts and Sophie Monk. Brown’s and co-hosts replaced top hosts Kyle and Jackie O who moved to a rival station.

On 16 June 2015, it was confirmed that she would not return for the twelfth series of The X Factor and was replaced by Rita Ora. She began presenting Lip Sync Battle UK, the British adaption of Lip Sync Battle, on Channel 5 in January 2016, alongside Professor Green.

In 2016, Brown guest judged at The X Factor at the London auditions, standing in for Scherzinger, while she had other commitments. In 2016 she announced that the Spice Girls – except for Victoria Beckham and Melanie C – were working on new material and a 20th anniversary tour for 2017. The song “Song for Her” was later leaked online featuring the bandmembers. Plans for a reunion were dropped when Geri Halliwell announced she was expecting her second child. Brown also confirmed her return to The X Factor Australia replacing Minogue, after a three-year absence. As only three categories were announced, she got a new category, Underdogs, where she chose an eliminated act from each of their categories to bring back to form a new category. In 2017 she returned to Broadway to star in the musical Chicago as Roxie Hart. Around the same time, she returned to acting in the movie Chocolate City: Vegas Strip guestarring Robert Ri’chard, Michael Jai White, Mekhi Phifer, Vivica A. Fox and Ginuwine. The same month, she had made a cameo in the movie Killing Hasselhoff guest-starring David Hasselhoff and Justin Bieber. In late 2017, Brown had a cameo in the music video for “Spice Girl” by Aminé.

In March 2017, Brown filed for divorce from Belafonte. They separated in December 2016. Brown accused Belafonte of “emotional and physical abuse”. In court, Belafonte’s representative said that due to the couple’s “extravagant and affluent” lifestyle, Brown had “wiped out all her Spice Girls money – approximately $50 million (£38.3 million), if not more”. The divorce was finalised on 15 December 2017. She cited her divorce from Belafonte and her father’s death as her reasons for seeking treatment for PTSD. In November 2018, Brown became a patron of the domestic violence surivors’ charity, Women’s Aid.

On 5 November 2018, Mel B announced the Spice Girls reunion tour on her Instagram profile. It was confirmed that Mel B and ex-bandmates Melanie C, Emma Bunton and Geri Halliwell—but not Victoria Beckham, who Mel B dressed as for Halloween the previous week — would return for a 13-date UK and Ireland stadium tour Spice World – 2019 Tour, their first for a decade.

In December 2018, Brown fell down some stairs, breaking several ribs and suffering a serious cut to her hand, for which she underwent emergency surgery.