The Spice Girls star, who confirmed her engagement to the Formula One boss last November, was pictured on the steps of St Mary's Church in Woburn, Bedfordshire wearing a bridal gown and veil.
Halliwell was joined by her nine-year-old daughter Bluebell, who wore a bridesmaid's dress and a floral crown in her hair.
In the lead up to the ceremony, the singer had shared pictures of her jewellery and dress with fans on Instagram.
She captioned each snap with a line from the traditional bridal custom: "Something old, something new. Something borrowed, something blue."
Halliwell first became friends with Horner in 2009 and the pair began dating in early 2014, following Horner's split from long-term partner Beverley Allen.
Only one of the singer's bandmates, Emma Bunton, attended the ceremony, with her sons Tate and Beau Lee acting as page boys.
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Victoria Beckham, Melanie C and Mel B are currently out of the country, but they took to Twitter to share old photos from the band's heyday and wish their friend the best on her big day.
Several big names from Formula One were among the guests on the groom's side, including Sir Jackie Stewart, Eddie Jordan and David Coulthard.
Dawn French and Jennifer Saunders - who both starred in the video for the Spice Girls' Comic Relief single, 'Who Do You Think You Are' - were also pictured arriving at the church, along with Britain's Got Talent judge Amanda Holden and presenter Myleene Klass.
