McCollum was the 10th overall pick in the NBA draft out of Lehigh, where he averaged 21.3 points, 6.3 rebounds, 2.7 assists and 2.05 steals over four seasons. He scored 2,361 career points, making him the all-time leader for the Patriot League.
The 6-foot-3 point guard was introduced by the Blazers at a news conference on Monday. He is expected to play in the NBA Summer League starting Saturday.
Terms of the contract announced Thursday were not released.
The blazers also formally signed free agent guard Earl Watson on Thursday.
The 12-year NBA veteran played the past three seasons with the Utah Jazz. He played in 48 games last season, averaging 17.3 minutes and two points, 1.8 rebounds and four assists.
Watson has also played in Seattle, Memphis, Denver and Oklahoma City.
Information from The Associated Press was used in this report.