Waseem Baloch, 25, was arrested in Dera Ghazi Khan in central Pakistan on Saturday night.
The Dawn newspaper said he had confessed to the murder, saying he drugged and strangled her "for dishonouring the Baloch name".
Qandeel Baloch, 26, became a household name for posting sometimes raunchy photographs, comments and videos.
She recently caused controversy by posting pictures of herself alongside a Muslim cleric.
he paper quoted Waseem Baloch as saying: "She wasn't aware I was killing her. I gave her a tablet and then strangled her."
Police said the brother had escaped to Dera Ghazi Khan after the killing in the Karimabad area of Multan early on Saturday morning.
They said he fled with two friends who were still being sought.
Ms Baloch was buried on Sunday morning in her ancestral village near Dera Ghazi Khan in Punjab province. Images from the scene showed scores of people attending the services.
Mufti Qavi, who said he had forgiven Ms Baloch for her actions, had offered to lead the funeral prayers, reports said.