McCollum is still owed $57 million over the next two seasons before the extension begins in 2021-22.
The 27-year-old has developed into one of the most reliable scorers in the Association alongside superstar point guard Damian Lillard. Together, they led Portland to its first Western Conference finals appearance since 2000 this past season.
Lillard also agreed to remain with the Blazers long term this summer when he signed a four-year, $196-million super-max extension.
In 2018-19, McCollum averaged 21 points, four rebounds, and three assists across 70 appearances. He amped up his production during Portland's playoff run, averaging 24.7 points in 16 contests.