William Lonsdale (2[1] or 21[2] October 1799 – 28 March 1864)[1] supervised the founding of the official settlement at Port Phillip (later named Melbourne) from 1836 and went on to serve under the Superintendent La Trobe from 1839 to 1854.

Lonsdale was born in Den Helder,[2] Batavian Republic, during Britain's failed campaign to restore the deposed Prince William of Orange.

He immediately appointed Captain William Lonsdale as Chief Agent of Government, Police Magistrate and Commandant for the Port Phillip region.

Lonsdale's Chief Agent duties were authorised in written instructions from Governor Sir Richard Bourke: With reference to part of Captain Lonsdale's instructions inform the Collector of Customs and Surveyor-General that owing to the distance of Port Phillip from Sydney and the difficulty of frequent communication, it has been thought proper to give the Police Magistrate authority to act for the Government in certain cases and therefore direct them to instruct their officers proceeding to Port Phillip to attend to such orders as they shall receive from Captain Lonsdale which will be their sufficient warrant and to apply to him for advice and assistance in any case of doubt or difficulty or when anything is required by them out of the usual course of service.

Colonial secretary Alexander McLeay followed this instruction with a written appointment for Lonsdale stating that the Governor had placed his entire confidence in his intelligence and discretion by giving him the General Superintendence of the new settlement over all matters that should require the immediate exercise of Government authority on the spot.

His instructions also contained specific reference to the Aboriginal natives in which he was to conciliate them by kind treatment and presents, protect them from any manner of wrong, maintain friendly relations with them and improve by all practical means their moral and social conditions.

It also indicated that Captain William Lonsdale was held in high esteem by Governor Sir Richard Bourke who had personally chosen him to manage this Port Phillip settlement foundation.

Lonsdale had to establish a new remote settlement that was only accessible by sea, as no overland route existed from Sydney to Port Phillip, as southern New South Wales was a vast forest with large rivers, yet to be explored.

This speed reflected Bourke's concerns about the 200 illegal settlers at Port Phillip, who were claiming land and negotiating with the aboriginal natives for other areas.

Lonsdale finally arrived at Port Phillip with his wife Martha, daughter Alice and his one assigned servant, on board HMS Rattlesnake, commanded by Hobson (later Governor of New Zealand).

Here Captain William Lonsdale was met by John Batman and Dr Thompson and other assembled illegal settlers, all anxious to have their land claims and investments validated.

Besides Lonsdale's duties for the immediate exercise of authority of the government, and his Confidential Reports to the Governor, he was to take a census, noting land occupation and aboriginals.

Charles Joseph La Trobe arrived in Melbourne in October 1839 as Port Phillip's first Superindendant and he relieved Captain William Lonsdale of his General Agent of Government duties.