 Knibbs joined the New South Wales Land Survey Department in 1877 and in January 1878 was appointed a licensed surveyor.In 1889 Knibbs resigned to take up private practice as a surveyor, and in 1890 became lecturer in surveying at the University of Sydney.Knibbs was elected a member of the Royal Society of New South Wales in 1881, became a member of the council in 1894, from 1896 to 1906 was almost continuously honorary secretary, and in 1898-9 was president.