In April 1835[3] he married his second cousin Sophie Augusta Collett (1811–1872).[1] Sophie Augusta Collett was the daughter of Johan Collett and niece of Jonas Collett, both of whom were Constitutional founding fathers. In addition she was the sister of Peter Jonas Collett, and as such sister-in-law of writer Camilla Collett. Their son Peter Steenstrup became a military officer as well. He married Marie Hiorth Kielland in July 1873.[3]
Peter Severin Steenstrup was buried at the Vår Frelsers gravlund. A street in Oslo, Steenstrups gate was named for him.[6]