Background
Dempster was born in Fremantle, Western Australia, to James McLean Dempster, a sea captain, and Ann Ellen Pratt.
Dempster was born in Fremantle, Western Australia, to James McLean Dempster, a sea captain, and Ann Ellen Pratt.
He was educated at Lowe"s School in Fremantle and at Reverend Dacres Williams" School in Guildford.
A farmer and grazier by trade, he was also one of the first European explorers of the Esperance district as well as a councillor and chairman on the Toodyay and Northam Road Boards for many years. In 1870 the brothers developed a station at Fraser Range with the assistance of ticket of leave men from Perth who were employed to develop the station land and build various stone structures. The station had been founded by John and Alexander Forrest on their way to Adelaide, and was the first sheep station on the Nullarbor Plain.
In 1871, the Dempsters acquired the cutter Gypsy which was used to sail wool to Adelaide, stores and stock from Fremantle and hunt seals at the islands off Esperance.
In 1872, he inherited a property at Northam and Toodyay, and was elected to the Toodyay Road Board, on which he served until 1885. On 11 March 1873, he was elected at a by-election to the Toodyay seat in the Legislative Council, which he held until 29 September 1874.
In 1886, after selling the steam mill and store to George Throssell, Dempster purchased the 1,560 acres (630 ha) Springfield estate near Northam, and farmed at Wongamine. In 1888, he was made a Justice of the Peace.
He was to hold the seat until his death while visiting Sydney on 22 July 1907.
He was buried at the Northam cemetery.
In 1880, Dempster won awards at the Melbourne Colonial Exhibition for flour produced at the mills. Following a failed attempt to secure the Legislative Assembly seat of Toodyay in the inaugural elections under responsible government in 1890, he won the highest vote and a six-year term in the Legislative Council for the East Province when that body became fully elective in July 1894.
He became prominent in horse breeding and racing and helped to found the Northam Race Club, later becoming its secretary. He also was a member of the prestigious Western Australian Turf Club, which provided a meeting place for many of the Colony"s leading men of that time.