Crawford broke the news earlier Thursday when he posted "Rip city!!!" on his Twitter account.
The 6-foot-5, 200-pound guard has spent the last two seasons with the Atlanta Hawks. Crawford averaged 14.2 points and 3.2 assists in 76 games last year.
He won the NBA's Sixth Man award in 2009-10 after averaging 18.0 points and 3.0 assists in 79 contests.
"We've thought highly of Jamal for a long time and think he's a great fit for our team," said Trail Blazers acting general manager Chad Buchanan. "He brings a scorer's touch and veteran leadership that will help us immediately."
Crawford has averaged 15.4 points, 2.6 rebounds and 3.9 assists in 752 career games (393 starts) with the Bulls, Knicks, Warriors and Hawks.