Mitchelson was born in Auckland in a cottage on Queen Street in the mid 1840s.

[1] He developed business interests in timber and kauri gum, shipbuilding, and horse racing and breeding.

[4] Mitchelson was the Mayor of Auckland City from 1903 to 1905,[5] chairman of the Remuera Road Board,[1] and a member of the Legislative Council from 1920 until his death on 11 April 1934.

[7] He was buried at Purewa Cemetery in the Auckland suburb of Meadowbank.

[8] Mitchelson had a wooden mansion built at Muriwai around the year 1902, which he named Oaia, named after Oaia Island.