About 14 km wide at its narrowest, it was formed by the rising sea around 13,000 years ago, at the end of the Pleistocene era, when it submerged the land connecting what is now Kangaroo Island with the Fleurieu Peninsula.

Backstairs Passage was named by Matthew Flinders on 7 April 1802 whilst he and his crew on HMS Investigator were exploring and mapping the coastline of South Australia.

Due to the relatively shallow Gulf St Vincent joining the Southern Ocean through the deeper Backstairs Passage, this narrow and dangerous channel is subjected to strong currents, heavy tidal swells and steep breaking seas.

[4] In the early years following European colonisation many of the nearly fifty vessels wrecked in the hazardous waters around Kangaroo Island were lost while crossing Backstairs Passage to and from the mainland.

[6] On 6 June 1995, South Australian marathon swimmer Andrew Martin completed the first recorded solo crossing of Backstairs Passage, covering the 14.25 km distance in 4 hours 31 minutes 30 seconds.