Williams, who was waived Thursday by the Dallas Mavericks, is the backup point guard the Cavs have coveted.
The three-time All-Star will back up Kyrie Irving and provide veteran leadership and poise off the Cavs bench. Williams, 32, had considered joining Utah, where he still has a home, but on Saturday confirmed to a league source that he would join the defending champions.
There were no takers on the waiver wire for Williams and what's left of his $9 million contract, though it is believed Williams' powerful agent, Jeff Schwartz, warned interested parties not to claim his client -- who wanted to join Cleveland.
There were at least eight teams believed to have the cap space to claim Williams via waivers, and at least one -- the Jazz -- tried to trade for him. Utah has a great chance to reach the playoffs and is below the minimum payroll teams are required to spend each season.
Five teams are under the $84.7 minimum payroll, including the Jazz, Denver, Philadelphia, Minnesota and Brooklyn.