The two-hour event will air on several networks at 8 p.m. ET, hosted by George Clooney in Los Angeles, Wyclef Jean in New York and CNN's Anderson Cooper in Haiti.
Sting will be joined in New York by Bruce Springsteen, Mary J. Blige, Jennifer Hudson and Shakira.
Timberlake and Aguilera will take the stage in Los Angeles, along with Alicia Keys, Dave Matthews, John Legend, Stevie Wonder, Taylor Swift and a group performance by Keith Urban, Kid Rock and Sheryl Crow.
In London, the lineup includes Rihanna, Bono, Coldplay, Jay-Z and The Edge.