Adding Driskel gives Houston more depth given the uncertainty around Watson's future with the team. Watson, who asked for a trade in January, is facing 22 civil lawsuits alleging sexual assault and inappropriate behavior.
Driskel spent the 2020 season with the Denver Broncos but was released by the team earlier this month.
Driskel's one-year deal has a $1 million base salary with a $250,000 signing bonus and bonuses for playing time and for being on the Texans' 46-man game-day roster, according to his agents.
Last year with Denver, Driskel made three appearances, completing 54.7% of his passes for 432 yards with three touchdowns and two interceptions.