He is reportedly expected to remain with the NBA team instead of going to the G League, although he can only spend 45 days with the Cavs before they must sign him to an NBA deal.
Rookie first-round pick Collin Sexton will likely become the starter during this stretch while Jordan Clarkson can also spend time at the point, although this move adds much-needed depth in the backcourt.
Harrison was waived by the Memphis Grizzlies after just one game this season, scoring two points in five minutes.
He had made a much bigger impact in the last two years with Memphis after being taken in the second round of the 2015 draft. The 24-year-old started 46 of the 56 games he played last season, averaging 9.5 points and 3.2 assists per game.
Overall, the Kentucky product has averaged 7.4 points in 129 career appearances.
On a Cavs team that has a 1-10 record to start the year, Harrison could be a useful addition.