Halliwell – better known as Ginger Spice – is one of a number of stars treading the boards to perform in West End musicals in aid of the annual fund-raiser.
She will be joined by X Factor winner Alexandra Burke, boy band Blue, soul singer Macy Gray and newcomers Stooshe in Pop Goes the Musical.
Halliwell, who will take to the stage of London's Palace Theatre on 25 October to perform in Singin' In The Rain, said she was excited at being a part of the project.
She joked: "I have a thing for rain, so I'm very excited to be performing in this particular musical, and it's all for BBC's Children In Need.
Just imagine, for one night I get to perform in this classic show!"
Blue will don the famous red coats from 1960s set musical Jersey Boys on October 11, describing it as "an amazing chance".
Les Misérables will welcome Burke centre stage on September 18.
She said: "To join the cast of one of the West End's most famous musicals is a real honour."
Thriller Live audiences will be treated with two separate performances on 15 November by Grammy Award-winning artist Macy Gray and chart-toppers Stooshe.
Tickets for all performances cost £80 with 50% of each sale going to the charity.
Meanwhile, actress Angela Griffin and songstress Jesse J have lent their support to the Show You Care With the Lindt Bear campaign, which aims to raise £100,000 for the charity.
To help reach this target 20 celebrities have signed a porcelain version of the trademark chocolate bear for an online auction.