A descendant of the Dukes of Roxburghe and cousin of Allan Ebenezer Ker, Robert was born in Dalkeith and educated in Scotland, and came to Vancouver Island in 1859. He was friendly with colonial governor Sir James Douglas and John Sebastian Helmcken. Ker was the auditor general of the first Colony of British Columbia and also acted as auditor general of the Colony of Vancouver Island. When the two colonies united in 1866, he continued in the position of auditor general.
The Ker Memorial Wing of the Art Gallery of Greater Victoria is named in his honour.
In 2009 the Ker Family celebrated its 150th anniversary in British Columbia.