Grizzlies general manager Zach Kleiman and Brown finalized details on the agreement ahead of a 6 p.m. ET deadline for the 2018 draft class. Jackson planned to sign the contract Monday morning at the Grizzlies' practice facility.
Jackson, 22, has emerged as a cornerstone player on a gifted, young Grizzlies roster and has shown himself to be one of the most versatile and dynamic young big men in the league.
Jackson was the No. 4 pick out of Michigan State in the 2018 NBA draft and has partnered with point guard Ja Morant to construct one of the most promising young duos in the league.
Jackson missed a significant part of the 2020-21 season recovering from a meniscus injury but has returned to full strength this preseason. He has averaged 15.4 points, 4.7 rebounds and 1.5 blocks in his three NBA seasons.
The deadline for class of 2018 rookie extensions is Monday, and so far, Atlanta's Trae Young, Dallas' Luka Doncic, Oklahoma City's Shai Gilgeous-Alexander, Denver's Michael Porter Jr., Phoenix's Mikal Bridges and Boston's Robert Williams III are among the players who've agreed to extensions.