State politics

McLachlan was elected to the South Australian Legislative Council at the 2014 state election for an eight-year term.^[7][8]

In March 2015, the 99-year grave licence at Centennial Park for an ANZAC World War I veteran who had fought at Gallipoli expired. No family was located to pay for the continuation of the lease, and there was a possibility of the site being reused. As a fellow veteran, McLachlan paid the licence renewal fee to preserve the historical site.^[9]

In July 2015, McLachlan crossed the floor and voted against the Statutes Amendment (Serious and Organised Crimes) Amendment Bill 2015, better known at the time as the 'Bikies Bill', which was contrary to the Liberal Party's position at the time. McLachlan had argued that Parliament should not act like a court and the provision in the Bill breached the principle of the separation of powers. He was the only Liberal Member of Parliament to vote against the Bill.^[10] McLachlan is a strong supporter of the rule of law.

In late 2015 McLachlan introduced a Bill that would give legal protections to the identity of individuals who provide sensitive information to journalists. This is a common protection in other Australian jurisdictions, however; in South Australia the current law requires journalists to identify sources during court proceedings or commissions of inquiry, otherwise face a potential prison sentence.^[11] The Bill was ultimately not supported by the Government.

In August 2017, McLachlan introduced an amendment to a motion put forward by the SA Greens and Advance SA MLCs calling for the Australian Government to 'recognise the State of Palestine, as we have recognised the state of Israel, and announce the conditions and timelines to achieve such recognition.'^[12] McLachlan's amendment called 'on both sides to resume direct negotiations in good faith' and 'on the Commonwealth government to recognise the state of Palestine once the two sides have successfully negotiated a two-state solution, as required by international law.' This amended motion was passed by the South Australian Legislative Council and welcomed by many Jewish organisations including the Australia/Israel Jewish Affairs Council, the Executive Council of Australian Jewry and the Jewish Community Council of South Australia.^[13][14]

At the time of moving his successful amendment, McLachlan told Members of the Legislative Council:

In the land of questionable regimes that are often founded on intolerance, Israel has a vibrant democracy that operates under rule of law and is innovative and prosperous. For Israel to have the security, it needs a viable Palestinian state, a Palestinian state that recognises Israel and rejects violence against the Jewish people. In my own lifetime, I dream of seeing a state of Palestine working cooperatively and collaboratively with its neighbour. Palestinians of all factions must reject violence.

On 3 May 2018, McLachlan was nominated to serve as President of the South Australian Legislative Council being elected by the Members of the Legislative Council unopposed.

Federal politics

On 1 February 2020, McLachlan was selected by the South Australian Liberal Party to fill a vacant seat in the Australian Senate caused by the resignation of former Liberal Senator Cory Bernardi. McLachlan defeated former Law Council of Australia president Morry Bailes and former state party treasurer Michael van Dissel.^[15][16] He resigned as president and a member of the Legislative Council on 5 February 2020, and was appointed to the Senate by a joint sitting of the South Australian Parliament the following day.^[4] He served the remainder of Bernardi's term expiring on 30 June 2022, and was re-elected for another six year term at the 2022 federal election.

McLachlan is a member of the Centrist faction of the Liberal Party,^[17] after previously being aligned with the Moderate/Modern Liberal faction during the Morrison government years.^[18]