Howard a 15-year veteran, averaged 4.1 points in 42 games with Denver and Charlotte last season.
Terms were not disclosed.
"Juwan Howard will add a wealth of experience and veteran savvy to our young, talented roster," Blazers general manager Kevin Pritchard said in a statement. "We look forward to Juwan's contributions on the court and in the locker room."
The 6-foot-9 power forward was the 14th player added to the Blazers roster in advance of fall camp. The Blazers have looked this offseason at a number of big forwards, including Stromile Swift and Greg Ostertag, before going with Howard.
Howard, 36, has averaged 14.9 points and 6.6 rebounds in 1,043 games. He has appeared in the playoffs four times, averaging 9.8 points, 5.7 rebounds and 1.2 assists.
Howard was the fifth player selected in the 1994 draft.