Marcel McClinton, who graduated high school several months ago and officially launched his campaign in July, said he was at the convenience store when the thief allegedly stole beer, KTRK reported
McClinton said he and three other customers chased the man down the street and cornered him behind some bushes until police arrived, the television station reported.
"Someone just tried to stab me and 3 other guys," McClinton wrote on Twitter.
"He stole a gun, ran off and then pulled a knife on them while they chased him outside," KTRK reported, quoting police dispatchers.
McClinton is a survivor of the 2016 mass shooting at the Memorial Drive United Methodist Church, Houstonia magazine reported. For the past two years, McClinton has campaigned for gun-violence prevention laws in Austin and Washington, D.C., the magazine reported.
McClinton kept his Twitter followers up to date on the Thursday night incident.
"I'm safe. Suspect in custody. No one was injured. Thank you all for checking in," McClinton tweeted.