Barrett-Lennard arrived at the Swan River Colony on board the Marquis of Anglesea on 23 August 1829 bringing with him six servants, farm animals, and equipment.
He was allotted a relatively large grant of 1,176 hectares (2,906 acres) and quickly established a property in the virgin bushland in the West Swan Area near Guildford which he named St Leonard's.
[2] In December 1829, the Lieutenant-Governor, James Stirling appointed him, along with five other prominent settlers, a Justice of the Peace.
[4] On 4 May 1840, Barrett-Lennard replaced William Locke Brockman as one of the four nominee positions on the Western Australian Legislative Council.
He only held the position until the following year before resigning, possibly due to a fire which destroyed the St. Leonards homestead in 1841.