Barlow has enlisted Williams, Dizzee Rascal and Little Mix for one of the shows, while a second concert will include Ellie Goulding and Rizzle Kicks.
The Children in Need Rocks 2013 shows are being staged at London's Hammersmith Apollo, recently renamed the Eventim Apollo, in November.
Chris Evans and Fearne Cotton will be the hosts for the shows which will be compiled for a BBC1 programme later in the month.
The show headlined by Williams takes place on November 12, while the Goulding concert - also featuring Bastille and Passenger - is on the following evening.
Barlow said the shows would be "bigger and better than ever - doing not one, but two concerts" and said he may be performing.
He said: "There are still some great acts we're keeping up our sleeve to announce in the coming weeks and there will be a couple of surprise moments on stage as well. And who knows, I might even get up on stage too."
Barlow is to release his third solo album on November 25 - just a week after Williams issues his next collection Swings Both Ways.
Tickets for the concert go on sale tomorrow with further details at bbc.co.uk/pudsey.