Blum is expected to be behind the microphone for about 60 games a year this year, filling the role of color analyst when Bill Brown isn't in the booth. Former Astros catcher Alan Ashby is returning to Houston this year to work alongside Brown, and he will slide into the play-by-play role when Brown is off.
An official announcement could come next week.
A popular player in Houston, Blum, 39, played with six teams in his 14-year Major League career, including five seasons with the Astros (2002-03 and 2008-10). He spent his last two seasons with the D-backs, but was limited to 40 games because of injury.
The versatile Blum is probably best remembered by Astros fans for hitting the game-winning home run for the White Sox in the 14th inning of Game 3 of the 2005 World Series at Minute Maid Park.
Houston's TV booth is being shuffled following the departure of long-time color analyst Jim Deshaies to the Cubs last month.
Ashby returns to Houston after calling games for the Blue Jays for the previous six seasons. He worked alongside Hall of Fame announcer Milo Hamilton in the radio booth from 1998-2006 in Houston. Hamilton returned from a full-time role following season.
The Astros are still in the market for two radio announcers and have interviewed several candidates, including former player Steve Sparks. The team didn't renew the contracts of play-by-play voices Brett Dolan and Dave Raymond, who were with the club for seven seasons.
Ashby, 61, played 17 years in the Major Leagues, including 11 with the Astros (1979-89). He's a career .245 hitter with 90 homers and 513 RBIs, logging 69 homers and 388 RBIs with the Astros. He also caught a pair of no-hitters with the Astros.