Williams, who has played his entire seven-year career with Philadelphia, grew up 25 miles northeast of Atlanta in Snellville, Ga.
Financial terms of Williams’ deal were not announced by the Hawks.
Williams, 25, has career averages of 11.3 points, 3.0 assists, and 2.0 rebounds in 455 games.
Atlanta’s busy off-season has included trading Joe Johnson and Marvin Williams and acquiring guards Devin Harris, Anthony Morrow, Jordan Farmar and DeShawn Stevenson and forwards Jordan Williams and Johan Petro.
Williams led the Sixers in scoring last season with a career-best 14.9 average as the sixth man.
The Hawks were waiting for the NBA to approve the signing before they announced the trade.
THUNDER: Starting center Kendrick Perkins is expected to be ready for next season after having surgery on his right groin Thursday.
The team announced that the procedure was a success and that Perkins will miss four to six weeks before returning to normal off-season activities.
Perkins partially tore the groin in Game 4 of the Thunder’s first-round playoff sweep of Dallas, although Oklahoma City withheld the extent of his injury until after the season. At the time, the Thunder only called it a strained hip muscle.
PACERS: Are sending point guard Darren Collison and wing player Dahntay Jones to the Dallas Mavericks for center Ian Mahinmi, according to the agent for one of the players.
Mark Bartelstein, who represents Jones, confirmed that the deal is in place.
“That’s going to happen,” Bartelstein said.
The Mavericks are also adding 7-foot center Chris Kaman.
BOBCATS: Have agreed to a two-year contract with former Los Angeles Lakers point guard Ramon Sessions, a person familiar with the situation said.