Financial terms were not disclosed for the deal, which will keep Mancz with Houston through the 2020 season.
An undrafted free agent out of Toledo in 2015, Mancz is entering his fourth season with the Texans.
The 6-foot-4, 310-pound Mancz appeared in 10 games, making seven starts, during the 2017 season. He started five games at center and made two starts at right guard.
The 26-year-old Mancz started all 16 regular-season games and two postseason contests at center in 2016. He was the only lineman on the club to start every game.
As a rookie, Mancz appeared in three games before he was placed on season-ending injured reserve in early November. For his career, Mancz has started 23 of 29 games.
Mancz played four seasons at Toledo (2011-14) before signing with Houston.