The Astros, who move to the American League next season, plan to announce the move Thursday morning, the website reported, citing anonymous major league sources. The Astros have scheduled a news conference for 11 a.m. ET.
Porter will stay with the Nationals, who already have clinched a playoff berth, until their postseason is completed, sources told Fox.
The Astros, the worst team in the majors at 51-105, fired manager Brad Mills on Aug. 18 and replaced him a day later with Tony DeFrancesco on an interim basis.
Porter previously has interviewed for managerial openings with the Marlins and Pirates. He played in 89 major league games between 1999-2001 with the Cubs, A's and Rangers.
DeFrancesco told The Associated Press after Wednesday's game that he's been guaranteed a job somewhere in the organization next season, regardless of the outcome of the managerial search.