As well as performing at the actual BRIT Awards, the trio will headline a concert at London's O2 Shepherd's Bush Empire on Monday, 23 February.
There are 2,000 tickets up for grabs and they go on general sale Friday, 23 January at 9am. Pre-sale for O2 Priority Tickets starts Wednesday, 21 January at 9am.
Tickets are £75.
Funds raised go towards children and young people affected across war zones in Iraq, Syria, Democratic Republic of Congo, Afghanistan, Uganda and Central African Republic.
Ben Knowles, Director of Music at Warchild, said: "War Child are delighted to welcome back Gary together with Mark and Howard to London's O2 Shepherd's Bush Empire and to announce Take That as our headliners for 2015.
"It's going to be an incredible night for 2,000 lucky fans and an important one for the thousands of children it will help War Child save from the horrors of war."
Gary Barlow, Mark Owen and Howard Donald will also perform at the BRIT Awards ceremony at London's O2 Arena two days later, marking the band's sixth live appearance.
Of course, it will be their first as a trio, following the departure of Jason Orange at the end of last year. Other performers at the BRITs include Ed Sheeran, Sam Smith, Paloma Faith and Taylor Swift.
Sam leads the way with a huge five nominations, including 'Male Solo Artist of the Year' and 'Album of the Year'. Other multiple nominees include Ed Sheeran and George Ezra.
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