The deputy was shot at around 8:30 p.m. while inside his unmarked department vehicle. Authorities say several rounds were fired.
The deputy wasn't hurt, but his car was hit several times.
At the time, he was working a second job patrolling an apartment complex in west Houston, officials say.
"Hard working brothers and sisters in blue, working hard every day, leaving their families behind," Major Tony Huynh said. "And this, our deputy trying to earn extra income for his family and out here protecting the residents at this complex, being ambushed by a coward."
Deputies only have a vague description of a possible suspect seen standing nearby.
They're going through surveillance video in hopes of finding more clues.