Ellington, 25, averaged 10.4 points and 3.0 rebounds in 38 games with the Cleveland Cavaliers after being traded from the Memphis Grizzlies in midseason. Ellington has career averages of 6.9 points and 2.0 rebounds per game for three teams in four seasons.
The 6-foot-4, 200-pound Ellington likely will compete with fellow free-agent addition Devin Harris to start at shooting guard for the Mavs. O.J. Mayo, last season's starter at shooting guard, has agreed to a three-year, $24 million deal with the Milwaukee Bucks.
The signings can become official at 12:01 a.m. Wednesday, when the league lifts its annual moratorium on player business.