It is named for Captain Collet Barker, a British military officer and early explorer, prior to the British Settlement of South Australia, of the southern Mount Lofty Ranges, Fleurieu Peninsula and the region at the mouth of the Murray River near the Coorong where he died in 1831 whilst on active duty after successfully solo swimming the channel of water and went compass in hand over a sandhill.

The 63,886 km² seat currently stretches from Morgan in the north to Port MacDonnell in the south, taking in the Murray Mallee, the Riverland, the Murraylands and most of the Barossa Valley, and includes the towns of Barmera, Berri, Bordertown, Coonawarra, Keith, Kingston SE, Loxton, Lucindale, Mannum, Millicent, Mount Gambier, Murray Bridge, Naracoorte, Penola, Renmark, Robe, Tailem Bend, Waikerie, and parts of Nuriootpa and Tanunda.

For most of the first half-century after Federation, Barker included Glenelg and the Holdfast Bay area, and at times stretched as far as the inner metropolitan suburbs of Keswick and Henley Beach.

However, it became an entirely rural seat after parliament was expanded in the redistribution prior to the 1949 election when the new Division of Kingston was created based around Glenelg and the southern suburbs of Adelaide.

Seat-level opinion polls in the other two rural Liberal South Australian seats revealed NXT also leading in both Grey and Mayo.