Sheriff Ed Gonzalez said the federal operation happened at a home in the 2000 block of Edendale Circle in Katy on Thursday afternoon.
Major Ben Katrib said special agents with the DPS Criminal Investigations Division and members of the Gulf Coast Violent Offenders Task Force were conducting a felony warrant.
The suspect, described as a male in his 50s, was wanted for engaging in organized criminal activity out of Harris County and for aggravated assault out of Bexar County, Katrib said.
When officers knocked on the door and received no response, they forced entry and deployed a drone inside before hearing a single gunshot, according to Katrib.
Investigators say they breached the master bedroom window and found the wanted man with a self-inflicted gunshot wound, and he was pronounced dead at the scene.
Katrib said the Texas Rangers are leading the investigation with help from HCSO.