The official announcement is expected Wednesday night at the Holmby Hills fundraiser for President Barack Obama.
At the convention, Democrats will nominate Obama for a second term.
Democratic National Committee leaders say Villaragosa's presence at the gathering will place him in the national spotlight and place the Latino mayor front and center as Democrats try to woo Latino support for Obama and other candidates.
The chairwoman of the Democratic National Committee, Congresswoman Debbie Wasserman Schultz, told DNC members that Villaraigosa has empowered people during his career and will encourage engagement from Americans across the country.
Villaraigosa was elected mayor in 2005 and re-elected in 2009.