The Spice Girls star – who was previously married to Jimmy Gulzar between 1998 and 2000 and Stephen Belafonte from 2007 to 2016 – tied the knot with Rory McPhee at St Paul's Cathedral in London on Saturday.
Mel, 50, wore a traditional white gown, adorned with pearls for the wedding, while her new husband Rory, 37, wore a traditional Scottish tartan kilt.
The happy couple posed for pictures on the steps of the historic venue and shared a kiss.
A reception at The Shard was booked for after the ceremony.
Emma Bunton was the only Spice Girl in attendance, accompanied by husband Jade Jones and their son Beau, 17.
Other celebrities included Mel's sister Danielle Brown, Daisy Lowe, Katherine Ryan and Gaby Roslin.
There was no sign of Victoria Beckham, Geri Halliwell and Melanie Chisholm.
However, Victoria shared her well wishes via social media, posting on her Instagram Stories.
She wrote: "Congratulations @officialmelb and @rorymcphee on your special day! I couldn't be more excited for you both and wish you a lifetime of happiness! Kisses xx."
She also shared a photo of herself and Mel B at an event together and captioned it, "Sending you love @officialmelb. @rorymcphee is a very lucky man!"
Meanwhile, Mel's children Phoenix Chi, Madison and Angel Iris all attended the ceremony.
Mel and Rory have known each other for years but did not start dating until 2018 and they got engaged four years later.
Rory is a "family friend" of Mel's cousin, Christian Cooke, with the pair having gone to school together.
Speaking about the proposal, Rory previously told HELLO! Magazine: "I was so nervous, my lips were trembling. I'd spent ages writing down all these things I wanted to say but when it came to it, I just babbled."
Mel responded: "Oh no, it was lovely, what you said. He told me he loved me, that I was his best friend and that he wanted to be with me for the rest of our lives."
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