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 Under 25 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 Under 25 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 Summer 2012, Brown reunited with the Spice Girls for a one off performance at the 2012 Summer Olympics Closing Ceremony in London, performing on top of London Cabs to a medley of two of their best known hits, Wannabe and Spice Up Your Life. The performance was the most tweeted about moment from the whole ceremony. Later the year, the Spice Girls reunited again to launch and attend the premiere of Viva Forever! (Musical).

 

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In March 2013,it was confirmed that Brown would judge Australia's Got Talent along with fellow Brit 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 fellow Spice Girl Geri Halliwell to replace Brown.
Brown at Civic Hotel, in Australia.

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.

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. 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.

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Brown also confirmed her return to The X Factor Australia, after a three-year absence. As only three categories were announced, she got a new category, named, Underdogs, where she chose an eliminated act from each of their categories to bring back to form a new category.

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 and fellow new judge Heidi Klum as replacing Sharon Osbourne. Currently, she is judging alongside Mandel, Klum, and newcomer Simon Cowell, who replaced Stern in 2016.

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, Ginuwine and Melanie Brown. 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 Spice Girl by Aminé.

She gave her voice to the animated movie Blazing Samurai alongside Michael Cera, Samuel L. Jackson, Ricky Gervais, George Takei, Gabriel Iglesias, Djimon Hounsou, Michelle Yeoh, and Mel Brooks due for release in 2018.

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.