"It is only fitting, that after I served loyally for 19 years as Tim Duncan's assistant, that he returns the favor," a statement from Popovich reads.
Duncan played for the Popovich-led Spurs for all 19 of his NBA seasons, capturing five NBA titles, two MVP awards, and 15 All-NBA selections between 1997-2016.
The Spurs have faced uncommon instability over the three years since Duncan retired. Although the team won 61 games and appeared in the Western Conference finals during the 2016-17 campaign, San Antonio has failed to eclipse 50 wins or advance past the first round in each of the past two seasons.
Still, the organization has missed the playoffs just once in the past 30 years - during the 1996-97 season, which resulted in selecting Duncan with the No. 1 pick in the 1997 draft.
In other coaching news, the team announced Will Hardy has also been hired as an assistant coach.