[3] In December 1834, Leslie left London as a passenger aboard the convict transport Emma Eugenia, arriving in Sydney in May 1835.

By 1836 he was managing Collaroi, a property owned by his uncle, Walter Stevenson Davidson, in the Cassilis district of New South Wales.

Leslie was a poor manager however, and his activities drew criticism from his uncle, who was forced to sell the property to his relations, E. W. T. Hamilton and George Clive, by 1840.

[5] On his return to Sydney Leslie married Catherine (Kate), daughter of Hannibal Hawkins Macarthur, at Parramatta on 9 September 1840.

[5] In 1841 Leslie and his wife travelled from Sydney to Brisbane aboard the Hunter River Steam Navigation Company steamer, Shamrock.

[10] Leslie was elected as member of the NSW Legislative Assembly for the seat of Moreton, Wide Bay, Burnett and Maranoa from 19 November to 19 December 1857,[3][11] when the parliament was dissolved.

He purchased land in Waikato, where he established a productive farm and sheep stud at Wartle, just south of Hamilton, on New Zealand's North Island.

He was buried in plot 799[14] at St Thomas’ Anglican Church Cemetery in West Street, Crows Nest, Sydney.

These gates were taken from the Glengallan Homestead and re-erected in the Park to commemorate the centenary of the Leslie brothers establishing Canning Downs pastoral run.