The body of the 33-year-old was discovered at around 3 p.m. PT after paramedics were called to the residence in the 2900 block of Panorama Drive.
Sgt. Adam MacIntosh said Jarek Paderewski, who lives in Coquitlam, was not known to police prior to being arrested following the death of his sister. He was arrested at the scene.
"The motive for this homicide is not yet known and IHIT continues working with the Integrated Forensic Identification Section and the Coquitlam RCMP to collect evidence at the residence where the homicide occurred," MacIntosh said.
MacIntosh said Paderewski lives at the townhouse with his parents, but his sister did not.
Map: 2900 Panorama Drive, Coquitlam